Google hangouts: Bump to 5.4.2.0

Verified working with Firefox, however it still doesn't work with
Chromium because of the NPAPI vs PPAPI thing.

Chrome's Pepper Plugin API doesn't seem to look for
plugins in the MOZ_PLUGIN_PATH, anyway I left them there for others to
find the solution :-)
Merge pull request #3213 from wmertens/google-hangouts

Google hangouts: Bump to 5.4.2.0