[Snyk] Security upgrade puma from 6.4.0 to 6.4.2

[solipet]

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

Snyk has created this PR to fix one or more vulnerable packages in the `rubygems` dependencies of this project.

#### Changes included in this PR - Changes to the following files to upgrade the vulnerable dependencies to a fixed version: - Gemfile

⚠️ Warning

``` Failed to update the Gemfile.lock, please update manually before merging. ```

#### Vulnerabilities that will be fixed ##### With an upgrade: Severity | Priority Score (*) | Issue | Breaking Change | Exploit Maturity :-------------------------:|-------------------------|:-------------------------|:-------------------------|:-------------------------  | **581/1000**
**Why?** Recently disclosed, Has a fix available, CVSS 5.9 | HTTP Request Smuggling
[SNYK-RUBY-PUMA-6146928](https://snyk.io/vuln/SNYK-RUBY-PUMA-6146928) | No | No Known Exploit (*) Note that the real score may have changed since the PR was raised. Check the changes in this PR to ensure they won't cause issues with your project. ------------ **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/18f-wyj/project/b82c452c-7ea4-4d5c-8965-bf142f188184?utm_source=github&utm_medium=referral&page=fix-pr) 🛠 [Adjust project settings](https://app.snyk.io/org/18f-wyj/project/b82c452c-7ea4-4d5c-8965-bf142f188184?utm_source=github&utm_medium=referral&page=fix-pr/settings) 📚 [Read more about Snyk's upgrade and patch logic](https://support.snyk.io/hc/en-us/articles/360003891078-Snyk-patches-to-fix-vulnerabilities) [//]: # (snyk:metadata:{"prId":"08a6ae87-c7ae-4bb1-abbd-ed18c7c2055e","prPublicId":"08a6ae87-c7ae-4bb1-abbd-ed18c7c2055e","dependencies":[{"name":"puma","from":"6.4.0","to":"6.4.2"}],"packageManager":"rubygems","projectPublicId":"b82c452c-7ea4-4d5c-8965-bf142f188184","projectUrl":"https://app.snyk.io/org/18f-wyj/project/b82c452c-7ea4-4d5c-8965-bf142f188184?utm_source=github&utm_medium=referral&page=fix-pr","type":"auto","patch":[],"vulns":["SNYK-RUBY-PUMA-6146928"],"upgrade":["SNYK-RUBY-PUMA-6146928"],"isBreakingChange":false,"env":"prod","prType":"fix","templateVariants":["updated-fix-title","pr-warning-shown","priorityScore"],"priorityScoreList":[581],"remediationStrategy":"vuln"}) --- **Learn how to fix vulnerabilities with free interactive lessons:** 🦉 [Learn about vulnerability in an interactive lesson of Snyk Learn.](https://learn.snyk.io/?loc=fix-pr)

[Sgtpluck]

Closed in favor of https://github.com/18F/identity-dashboard/pull/728/