在执行任何 ruby 程序的时候都会出现这段，然后才是正常执行，求解

[/usr/lib/ruby/gems/1.9.1/specifications/rubyzip-0.9.9.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/launchy-2.2.0.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/netrc-0.7.7.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/heroku-2.35.0.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/heroku-api-0.3.7.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/excon-0.16.10.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/rest-client-1.6.7.gemspec] isn't a Gem::Specification (NilClass instead). [/usr/lib/ruby/gems/1.9.1/specifications/addressable-2.3.3.gemspec] isn't a Gem::Specification (NilClass instead).