我刚刚重新安装了ruby，现在我面临一些奇怪的错误。
$ ruby -v
ruby 2.0.0p645 (2015-04-13 revision 50299) [universal.x86_64-darwin15]
$ gem
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/psych.rb:205:in `parse': (<unknown>): mapping values are not allowed in this context at line 3 column 29 (Psych::SyntaxError)
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/psych.rb:205:in `parse_stream'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/psych.rb:153:in `parse'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/psych.rb:129:in `load'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/config_file.rb:319:in `load_file'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/config_file.rb:192:in `initialize'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/gem_runner.rb:66:in `new'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/gem_runner.rb:66:in `do_configuration'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/gem_runner.rb:46:in `run'
from /usr/bin/gem:21:in `<main>'
我不知道如何解决这个问题。有谁知道这个问题？