message: CHORE - update changelog.
diff: +## X.Y.Z (INSERT_DATE_HERE)
  +
  +#### Minor Changes
  +
  +- [Ability to de-serialize and serialize the GST instead of rebuilding it using Function.toString](https://github.com/SAP/chevrotain/issues/706).
  +
  +#### Bug Fixes
  +
  +- [Types - fixed groups parameter type in CustomPatternMatcherFunc](https://github.com/SAP/chevrotain/pull/751).
  +- [Types - CustomPatternMatcherFunc return type now allows null value](https://github.com/SAP/chevrotain/pull/746).
  +
  ## 3.5.0 (6-10-2018)
  #### Minor Changes
  