add explicit polymer version to make sure there is no conflict
add explicit polymer version to make sure there is no conflict

virajs/testrtc,webrtc/testrtc,shelsonjava/testrtc,ralic/testrtc,ralic/testrtc,webrtc/testrtc,virajs/testrtc,TribeMedia/testrtc,TribeMedia/testrtc,jessetane/testrtc,ralic/testrtc,jessetane/testrtc,jessetane/testrtc,TribeMedia/testrtc,jessetane/testrtc,TribeMedia/testrtc,virajs/testrtc,virajs/testrtc,shelsonjava/testrtc,ralic/testrtc,shelsonjava/testrtc,shelsonjava/testrtc