Fixed Xcode 5.1 libz link warning
Fixed Xcode 5.1 libz link warning

pichak/CocoaSPDY,johnkdoe/CocoaSPDY,twitter/CocoaSPDY,kouhao/CocoaSPDY,treejames/CocoaSPDY,johnkdoe/CocoaSPDY,kgoodier/CocoaSPDY,layerhq/CocoaSPDY,treejames/CocoaSPDY,kouhao/CocoaSPDY,pichak/CocoaSPDY,twitter/CocoaSPDY,treejames/CocoaSPDY,twitter/CocoaSPDY,kgoodier/CocoaSPDY,layerhq/CocoaSPDY,layerhq/CocoaSPDY