导航字体颜色：[self.navigationController.navigationBar setTitleTextAttributes:@{NSForegroundColorAttributeName: [UIColor whiteColor],
NSForegroundColorAttributeName : [UIFont boldSystemFontOfSize:18]}];
https://www.jianshu.com/p/c5f4e784848c 安装rvm
command line tool
OpenSSL
rvm
ruby
gem
cocoapods
https://blog.csdn.net/andy_jiangbin/article/details/79159716 头疼
