Bump android plugin to alpha8
Bump android plugin to alpha8

Summary: For Android Studio compat.

Reviewed By: emilsjolander

Differential Revision: D5489941

fbshipit-source-id: 4f8f95b776c7a26fbcb4df51a8f31da244155c97

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho