Bump rack-protection from 1.5.3 to 1.5.5

Bumps [rack-protection](https://github.com/sinatra/sinatra) from 1.5.3 to 1.5.5.
- [Release notes](https://github.com/sinatra/sinatra/releases)
- [Changelog](https://github.com/sinatra/sinatra/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sinatra/sinatra/commits)

Author: dependabot[bot]

Gemfile.lock

@@ -16,8 +16,8 @@ GEM
     mime-types-data (3.2021.0901)
     netrc (0.11.0)
     puma (2.15.3)
-    rack (1.6.4)
-    rack-protection (1.5.3)
+    rack (1.6.13)
+    rack-protection (1.5.5)
       rack
     rest-client (2.1.0)
       http-accept (>= 1.7.0, < 2.0)