Fix rubocop offenses

- Layout/TrailingWhitespace

```
actionpack/lib/action_controller/metal/request_forgery_protection.rb:49:4:
C: Layout/TrailingWhitespace: Trailing whitespace detected.
  #
   ^
```

Related to c3787494eda

- Performance/StartWith

```
tasks/release.rb:108:44: C: Performance/StartWith:
Use String#start_with? instead of a regex match anchored to the beginning of the string.
      header += "*   No changes.\n\n\n" if current_contents =~ /\A##/
```

1 files changed, 1 insertions, 1 deletions

diff --git a/tasks/release.rb b/tasks/release.rb
index f13342b90c..1e83814bae 100644
--- a/tasks/release.rb
+++ b/tasks/release.rb
@@ -105,7 +105,7 @@ namespace :changelog do
       current_contents = File.read(fname)
 
       header = "## Rails #{version} (#{Date.today.strftime('%B %d, %Y')}) ##\n\n"
-      header += "*   No changes.\n\n\n" if current_contents =~ /\A##/
+      header += "*   No changes.\n\n\n" if current_contents.start_with?("##")
       contents = header + current_contents
       File.write(fname, contents)
     end