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)

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

Author: dependabot[bot]

Gemfile.lock

@@ -20,7 +20,7 @@ GEM
       bson (= 1.12.5)
     netrc (0.11.0)
     rack (1.6.11)
-    rack-protection (1.5.3)
+    rack-protection (1.5.5)
       rack
     rest-client (2.0.0)
       http-cookie (>= 1.0.2, < 2.0)