Bump rack from 2.0.3 to 2.0.7

Bumps [rack](https://github.com/rack/rack) from 2.0.3 to 2.0.7.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.3...2.0.7)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -215,7 +215,7 @@ GEM
       method_source (~> 0.9.0)
     public_suffix (3.0.1)
     puma (3.11.0)
-    rack (2.0.3)
+    rack (2.0.7)
     rack-test (0.8.2)
       rack (>= 1.0, < 3)
     rails (5.1.4)