Fix regex that caused Mustermann::CompileError

exercism.io/vendor/bundle/ruby/2.3.0/gems/mustermann-1.0.0/lib/mustermann/regular.rb:40:in
`check_anchors': regular expression should not contain $:
"\\/submissions\\/(?<key>\\w+)\\/(nitpick$|(\\+?un)?like$)"
(Mustermann::CompileError)

exercism.io/vendor/bundle/ruby/2.3.0/gems/mustermann-1.0.0/lib/mustermann/regular.rb:40:in
`check_anchors': regular expression should not contain ^:
"^\\/submissions\\/(?<key>\\w+)\\/(nitpick$|(\\+?un)?like$)"
(Mustermann::CompileError)

app/routes/submissions.rb

@@ -52,7 +52,7 @@ class Submissions < Core
         redirect "/submissions/#{key}"
       end
 
-      get %r{^/submissions/(?<key>\w+)/(nitpick$|(\+?un)?like$)} do |key|
+      get %r{/submissions/(?<key>\w+)/(nitpick|(\+?un)?like)} do |key|
         redirect "/submissions/#{key}"
       end