Installing jasmine-core with jruby master:

./bin/jruby -S gem install jasmine-core

And then looking at the jasmine-core directory in my GEM_HOME (/Users/tambellini/.rvm/gems/jruby-1.7.4 for me) the jasmine-core directory (/Users/tambellini/.rvm/gems/jruby-1.7.4/gems/jasmine-core-1.3.1/) is empty.

After rolling back jruby master to 3dc5183 jasmine-core installs fine and has the contents of the gem in the directory. So the RubyGems 2.1 upgrade seems to be what caused it (7490f94).