message: Updated CHANGELOG.md for v3.1.0
diff: ## Change Log
  +### v3.1.0 (2020-02-18)
  +- [#122](https://github.com/sapientglobalmarkets/react-querybuilder/pull/122) Add prop to control value and operator reset functionality on field change. (@lakk1)
  +
  ### v3.0.1 (2019-12-06)
  - [#117](https://github.com/sapientglobalmarkets/react-querybuilder/pull/117) Fixed a rule default value on add/change (@xxsnakerxx)
  