Update README.md

updating version to 3.4.3 for SBAndroid testing

3.4.2-beta.1 test

Updating Cocos2D version to 3.4.1. This will be tagged release-3.4.1-…

…beta.1 and pulled into SB internal builds.

Setting version to 3.4.0

Updating VERSION and cocos2d.h to 3.3.7. Will tag this commit as the …

…3.3.7 commit.