You can clone with
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).
Looks like this is actually a rubygems issue as it happens on ruby-1.9.3-p385 too.
Actually, I will re-open this in the hope RG updates to fix this before we get 1.7.5 out. We should update if so:
Fixed by cee8f13.