[Snyk] Security upgrade ubuntu from 16.04 to xenial-20210416

[hengyin]

This PR was automatically created by Snyk using the credentials of a real user.

 ### Snyk has created this PR to fix 2 vulnerabilities in the dockerfile dependencies of this project. Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image. #### Snyk changed the following file(s): - `docker/decaf/Dockerfile` We recommend upgrading to `ubuntu:xenial-20210416`, as this image has only **93** known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected. #### Vulnerabilities that will be fixed with an upgrade: | | Issue | Score | :-------------------------:|:-------------------------|:-------------------------  | Allocation of Resources Without Limits or Throttling
[SNYK-UBUNTU1604-SYSTEMD-1320131](https://snyk.io/vuln/SNYK-UBUNTU1604-SYSTEMD-1320131) |   **614**    | Allocation of Resources Without Limits or Throttling
[SNYK-UBUNTU1604-SYSTEMD-1320131](https://snyk.io/vuln/SNYK-UBUNTU1604-SYSTEMD-1320131) |   **614**    | Allocation of Resources Without Limits or Throttling
[SNYK-UBUNTU1604-SYSTEMD-1320131](https://snyk.io/vuln/SNYK-UBUNTU1604-SYSTEMD-1320131) |   **614**    | Allocation of Resources Without Limits or Throttling
[SNYK-UBUNTU1604-SYSTEMD-1320131](https://snyk.io/vuln/SNYK-UBUNTU1604-SYSTEMD-1320131) |   **614**    | Improper Check for Dropped Privileges
[SNYK-UBUNTU1604-BASH-542609](https://snyk.io/vuln/SNYK-UBUNTU1604-BASH-542609) |   **536**   --- > [!IMPORTANT] > > - Check the changes in this PR to ensure they won't cause issues with your project. > - Max score is 1000. Note that the real score may have changed since the PR was raised. > - This PR was automatically created by Snyk using the credentials of a real user. --- **Note:** _You are seeing this because you or someone else with access to this repository has authorized Snyk to open fix PRs._ For more information: 🧐 [View latest project report](https://app.snyk.io/org/hengyin/project/bc8000db-3d25-45f2-bfc5-7a6d138e401c?utm_source=github&utm_medium=referral&page=fix-pr) 📜 [Customise PR templates](https://docs.snyk.io/scan-using-snyk/pull-requests/snyk-fix-pull-or-merge-requests/customize-pr-templates) 🛠 [Adjust project settings](https://app.snyk.io/org/hengyin/project/bc8000db-3d25-45f2-bfc5-7a6d138e401c?utm_source=github&utm_medium=referral&page=fix-pr/settings) 📚 [Read about Snyk's upgrade logic](https://support.snyk.io/hc/en-us/articles/360003891078-Snyk-patches-to-fix-vulnerabilities) --- **Learn how to fix vulnerabilities with free interactive lessons:** 🦉 [Allocation of Resources Without Limits or Throttling](https://learn.snyk.io/lesson/no-rate-limiting/?loc=fix-pr) [//]: # 'snyk:metadata:{"customTemplate":{"variablesUsed":[],"fieldsUsed":[]},"dependencies":[{"name":"ubuntu","from":"16.04","to":"xenial-20210416"}],"env":"prod","issuesToFix":[{"exploit_maturity":"No Known Exploit","id":"SNYK-UBUNTU1604-SYSTEMD-1320131","priority_score":614,"priority_score_factors":[{"type":"fixability","label":true,"score":214},{"type":"severity","label":"high","score":400},{"type":"scoreVersion","label":"v1","score":1}],"severity":"high","title":"Allocation of Resources Without Limits or Throttling"},{"exploit_maturity":"No Known Exploit","id":"SNYK-UBUNTU1604-SYSTEMD-1320131","priority_score":614,"priority_score_factors":[{"type":"fixability","label":true,"score":214},{"type":"severity","label":"high","score":400},{"type":"scoreVersion","label":"v1","score":1}],"severity":"high","title":"Allocation of Resources Without Limits or Throttling"},{"exploit_maturity":"No Known Exploit","id":"SNYK-UBUNTU1604-SYSTEMD-1320131","priority_score":614,"priority_score_factors":[{"type":"fixability","label":true,"score":214},{"type":"severity","label":"high","score":400},{"type":"scoreVersion","label":"v1","score":1}],"severity":"high","title":"Allocation of Resources Without Limits or Throttling"},{"exploit_maturity":"No Known Exploit","id":"SNYK-UBUNTU1604-SYSTEMD-1320131","priority_score":614,"priority_score_factors":[{"type":"fixability","label":true,"score":214},{"type":"severity","label":"high","score":400},{"type":"scoreVersion","label":"v1","score":1}],"severity":"high","title":"Allocation of Resources Without Limits or Throttling"},{"exploit_maturity":"Mature","id":"SNYK-UBUNTU1604-BASH-542609","priority_score":536,"priority_score_factors":[{"type":"exploit","label":"Functional","score":171},{"type":"fixability","label":true,"score":214},{"type":"severity","label":"low","score":150},{"type":"scoreVersion","label":"v1","score":1}],"severity":"low","title":"Improper Check for Dropped Privileges"}],"prId":"5c58e991-2bd4-41d1-93a5-9b603cab27e7","prPublicId":"5c58e991-2bd4-41d1-93a5-9b603cab27e7","packageManager":"dockerfile","priorityScoreList":[614,536],"projectPublicId":"bc8000db-3d25-45f2-bfc5-7a6d138e401c","projectUrl":"https://app.snyk.io/org/hengyin/project/bc8000db-3d25-45f2-bfc5-7a6d138e401c?utm_source=github&utm_medium=referral&page=fix-pr","prType":"fix","templateFieldSources":{"branchName":"default","commitMessage":"default","description":"default","title":"default"},"templateVariants":["updated-fix-title","priorityScore"],"type":"auto","upgrade":["SNYK-UBUNTU1604-BASH-542609","SNYK-UBUNTU1604-SYSTEMD-1320131","SNYK-UBUNTU1604-SYSTEMD-1320131","SNYK-UBUNTU1604-SYSTEMD-1320131","SNYK-UBUNTU1604-SYSTEMD-1320131"],"vulns":["SNYK-UBUNTU1604-SYSTEMD-1320131","SNYK-UBUNTU1604-BASH-542609"],"patch":[],"isBreakingChange":false,"remediationStrategy":"vuln"}'