CocoaPods指定版本号

下面是podfile指定版本号时的逻辑运算符：

Besides no version, or a specific one, it is also possible touse logical operators:
'> 0.1'    Any version higher than 0.1         0.1以上
'>= 0.1'   Version 0.1 and any higher version  0.1以上，包括0.1
'< 0.1'    Any version lower than 0.1          0.1以下
'<= 0.1'   Version 0.1 and any lower version   0.1以下，包括0.1
In addition to the logic operators CocoaPods has an optimisicoperator ~>:
'~> 0.1.2' Version 0.1.2 and the versions up to 0.2, not including 0.2 and higher  0.2以下(不含0.2)，0.1.2以上（含0.1.2）
'~> 0.1' Version 0.1 and the versions up to 1.0, not including 1.0 and higher      1.0以下(不含1.0)，0.1以上（含0.1）
'~> 0' Version 0 and higher, this is basically the same as not having it.          0和以上，等于没有此约束