Fix #379: action methods can be inherited now
Fix #379: action methods can be inherited now

mobxjs/mobx,mweststrate/MOBservable,andykog/mobservable,andykog/mobx,mweststrate/MOBservable,mobxjs/mobx,mobxjs/mobx,mweststrate/MOBservable,andykog/mobx,andykog/mobservable,mobxjs/mobx