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]>

Gemfile.lock

@@ -115,9 +115,6 @@ GEM
       mail (~> 2.2)
     erubis (2.7.0)
     eventmachine (1.0.8)
-    exception_notification (4.1.1)
-      actionmailer (>= 3.0.4)
-      activesupport (>= 3.0.4)
     execjs (2.7.0)
     factory_girl (4.5.0)
       activesupport (>= 3.0.0)
@@ -211,7 +208,7 @@ GEM
       slop (~> 3.4)
     racc (1.5.2)
     rack (1.6.13)
-    rack-protection (1.5.3)
+    rack-protection (1.5.5)
       rack
     rack-test (0.6.3)
       rack (>= 1.0)
@@ -389,7 +386,6 @@ DEPENDENCIES
   diff-lcs
   draper
   email_spec
-  exception_notification
   factory_girl_rails
   faker
   guard