docs(readme): add build badge in readme, close #3
docs(readme): add build badge in readme, close #3

REASON:
1. use github pull request as workflow
2. use travis-ci to do CI process

fex-team/swiper,fex-team/swiper,zhangbobell/swiper,zhangbobell/swiper,zhangbobell/swiper,fex-team/swiper