You don't have write permissions for the /System/Library/Frameworks/Ruby.framework/Versions/x.x/usr/lib/ruby/gems/x.x.x directory.

Gem Error

ERROR:  While executing gem ... (Gem::FilePermissionError)

    You don't have write permissions for the /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/gems/2.6.0 directory.

 

解决办法：