cocoapods版本更新

1.下载某些三方库时，pod install会出现错误

$ pod install
Analyzing dependencies
[!] The version of CocoaPods used to generate the lock file (1.0.1) is higher than the version of the current executable (1.1.0.beta.1). Incompatibility issues may arise.

2.需要更新Cocoapods

sudo gem update --system

提示错误：

Updating rubygems-update
ERROR:  While executing gem ... (Errno::EPERM)
    Operation not permitted - /usr/bin/update_rubygems

3.这是由于没有权限，执行以下代码，就可以了

sudo gem install -n /usr/local/bin cocoapods --pre 

4.查看此时cocoapods版本，成功了！！！

pod --version