InlineDiff: fix bug "unmatched close parenthesis"

lib/gitlab/inline_diff.rb

@@ -34,9 +34,8 @@ module Gitlab
           end
           last_the_same_symbols += 1
           last_token = first_line[last_the_same_symbols..-1]
-
-          diff_arr[index+1].sub!(/#{last_token}$/, FINISH + last_token)
-          diff_arr[index+2].sub!(/#{last_token}$/, FINISH + last_token)
+          diff_arr[index+1].sub!(/#{Regexp.escape(last_token)}$/, FINISH + last_token)
+          diff_arr[index+2].sub!(/#{Regexp.escape(last_token)}$/, FINISH + last_token)
         end
         diff_arr
       end