Update README.md

Migrate to AndroidX, flex box demo: #26 [ci skip]

update README.md

update canScroll(), new version: 1.9

refactor: sync hasStableIds

feat: func setHasStableIds and setOnStableIdCallback

update gradle tool sdk version

version: 1.7.0, support load failed view #17

test: update travis

new version, close #12