message: fixes CustomPatternMatcherFunc return type now allows null value
diff: @@ -1313,7 +1313,7 @@ export declare type CustomPatternMatcherFunc = (
  groups?: {
  [groupName: string]: IToken
  }
  -) => RegExpExecArray
  +) => RegExpExecArray | null
  /**
  * API #2 for [Custom Token Patterns](http://sap.github.io/chevrotain/docs/guide/custom_token_patterns.html).
  