tweaked define module to play a bit nicer with requirejs

In implementing skrollr into my requirejs modules per the README, I noticed that by giving the module a name, skrollr kept coming back as `undefined`. After drilling down a bit through the source code with another dev I found that by removing the naming of the define module, it was able to return the skrollr object to my requirejs modules. Interested to see if this is a fix that works for more people as well.