Remove emitter test warning

This addresses https://github.com/RobotWebTools/roslibjs/issues/74 . I'm not sure if there's a better way to do this given that it's another library that we depend on. It doesn't show up on devel, because that doesn't use mocha and  karma doesn't report window.consle messages. 

This patch will likely be needed on devel when mocha tests are added.