Closed #581: fixed a bug of cc.TMXLayer in v2.x that it can't display all map image when its type is hexagonal.
Merge pull request #1997 from dingpinglv/Iss581_HexagonalTilemapV2x

Closed #581: fixed a bug of cc.TMXLayer in v2.x that it can't display all map image when its type is hexagonal.