docs(CONTRIBUTING): revert is a modifier
docs(CONTRIBUTING): revert is a modifier

EG: https://github.com/angular/angular.js/commit/a582e708a2bb50358c19073fadc3be1048f6be06

Closes #12032

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js