[Snyk] Security upgrade capybara from 3.39.0 to 3.39.1

[JJediny]

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 :-------------------------:|-------------------------|:-------------------------|:-------------------------|:-------------------------  | **616/1000**
**Why?** Proof of Concept exploit, Has a fix available, CVSS 5.9 | Web Cache Poisoning
[SNYK-RUBY-RACK-1061917](https://snyk.io/vuln/SNYK-RUBY-RACK-1061917) | No | Proof of Concept (*) 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/tts/project/b7f6af61-3d0d-457d-b944-44f0f856e7da?utm_source=github&utm_medium=referral&page=fix-pr) 🛠 [Adjust project settings](https://app.snyk.io/org/tts/project/b7f6af61-3d0d-457d-b944-44f0f856e7da?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":"8171a3be-d75a-480b-a910-efb34d059a66","prPublicId":"8171a3be-d75a-480b-a910-efb34d059a66","dependencies":[{"name":"capybara","from":"3.39.0","to":"3.39.1"}],"packageManager":"rubygems","projectPublicId":"b7f6af61-3d0d-457d-b944-44f0f856e7da","projectUrl":"https://app.snyk.io/org/tts/project/b7f6af61-3d0d-457d-b944-44f0f856e7da?utm_source=github&utm_medium=referral&page=fix-pr","type":"auto","patch":[],"vulns":["SNYK-RUBY-RACK-1061917"],"upgrade":["SNYK-RUBY-RACK-1061917"],"isBreakingChange":false,"env":"prod","prType":"fix","templateVariants":["updated-fix-title","pr-warning-shown","priorityScore"],"priorityScoreList":[616],"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/