Bump to API 18
Bump to API 18

silentnuke/StickyGridHeaders,rchandnani/StickyGridHeaders,hgl888/StickyGridHeaders,java02014/StickyGridHeaders,kopihao/StickyGridHeaders,b2b2244424/StickyGridHeaders,bigsui/StickyGridHeaders,bboyfeiyu/StickyGridHeaders,inmite/StickyGridHeaders,HiWong/StickyGridHeaders,TonicArtos/StickyGridHeaders,guoxiaojun001/StickyGridHeaders