Fixed a typo in readme.
Fixed a typo in readme.

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