closed #3108: add -fsigned-char to make char to signed as default
Update travis.yml, only build master and develop branch [ci skip]
Merge pull request #4078 from minggo/iss3108-signed_char

closed #3108: add -fsigned-char to make char to signed as default on Android arm architecture
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into developAssetsManager