title: Custom Swiftlint rule to make Xcode warnings like depreciations as error
body: <p>My project do have around 3000 warnings, and my motive is to make our Xcode project warning free. I just started using swiftLint, As string.characters.count is depreciated, I wants to make each depreciation an error but step by step. I want to make it incremental so first I wants to focus on ".characters." usage removal throughout app. Even I can search in the project and remove it, but at the same time I do wanna set a rule that no other developer uses it in future. I tried the code below in my yml file, but Xcode isn't giving any error on .characters usage while compilation. I think I am using incorrect regex. Do anyone know what's wrong with the custom rule or the regex?</p>
  
  <pre><code>custom_rules:
    string_character_usage: # rule identifier
  included: ".*\\.swift" # regex that defines paths to include during linting. optional.
  excluded: ".*Test\\.swift" # regex that defines paths to exclude during linting. optional
  regex: ".*?!\\.characters.\\.*" # matching pattern // I think issue is here
  match_kinds: # SyntaxKinds to match. optional.
   - keyword
  message: "Please don't use .characters on string as it is already deprecated, take warnings seriously now." # violation message. optional.
  severity: error # violation severity. optional.
  </code></pre>