Add badges for Android Arsenal, minimum API level and Travis CI to README.
Add badges for Android Arsenal, minimum API level and Travis CI to README.

duaiyun1314/AwesomeValidation,thyrlian/AwesomeValidation,java02014/AwesomeValidation,thyrlian/AwesomeValidation,andyiac/AwesomeValidation,0359xiaodong/AwesomeValidation