Improve error message when not logged in

lib/bundler/gem_helper.rb

@@ -100,7 +100,7 @@ def rubygem_push(path)
       cmd << "--key" << gem_key if gem_key
       cmd << "--host" << allowed_push_host if allowed_push_host
       unless allowed_push_host || Bundler.user_home.join(".gem/credentials").file?
-        raise "Your rubygems.org credentials aren't set. Run `gem push` to set them."
+        raise "Your rubygems.org credentials aren't set. Run `gem signin` to set them."
       end
       sh_with_input(cmd)
       Bundler.ui.confirm "Pushed #{name} #{version} to #{gem_push_host}"