Bump dockerfile-rails from 1.5.12 to 1.5.14

Bumps [dockerfile-rails](https://github.com/fly-apps/dockerfile-rails) from 1.5.12 to 1.5.14.
- [Release notes](https://github.com/fly-apps/dockerfile-rails/releases)
- [Commits](fly-apps/dockerfile-rails@v1.5.12...v1.5.14)

---
updated-dependencies:
- dependency-name: dockerfile-rails
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -191,7 +191,7 @@ GEM
       thread_safe (~> 0.3, >= 0.3.1)
     diff-lcs (1.5.0)
     docile (1.4.0)
-    dockerfile-rails (1.5.12)
+    dockerfile-rails (1.5.14)
       rails (>= 3.0.0)
     dotenv (2.8.1)
     dotenv-rails (2.8.1)