Fix getStats and add an integration test.

This change also fixes a typo in the data channel integration test
and increments the webrtc-adapter dependency to the latest version,
which includes standardization of the getStats output format.

Note: this cannot be merged until after https://github.com/willscott/webrtc-adapter/pull/1 , because webrtc-adapter version 0.0.4 does not yet exist.