Fix failing testCoffeeScript

 # testCoffeeScript
 /builddir/build/BUILD/package/lib/nodeunit.js:72
         if (err) throw err;
                           ^
 Error: ENOENT, stat '/builddir/build/BUILD/package/testfixtures/coffee/mock_coffee_module.coffee'

Missing slash between 'test' and 'fixtures' causing the test to fail on Fedora 18/19 (running Node 0.10.5).