Minor improvements in array implementation
Minor improvements in array implementation

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