update MessageDisplayKit.podspec v0.2.7
fix the error Use of undeclared identifier "BYTE_SIZE" in FLAnimatedImage.m line 635

https://github.com/xhzengAIB/MessageDisplayKit/issues/120
fix the NSFoundationVersionNumber bug

fix https://github.com/xhzengAIB/MessageDisplayKit/issues/136
添加输入框样式调整例子