Hi, all: Just a test change suggestion. Would like to know what do you think. Using screenshot diff can test a lot of visual effects such as border/background-color/box-shadow, which can help improving our test coverage. I put a border-diff demo which is using `blink-diff` in this pull request https://github.com/apache/incubator-weex/pull/292 , the usage is as simple as just calling `util.diffImage` and make an assert.
Thanks. Adam Feng
