Travis CI: Upgrade to pylint 1.2.0

Just checking whether this will fix a very odd error reported by
Travis's pylint 1.1.0 (but not my own 1.1.0 running locally):

    stbt.py:1680: [E1120(no-value-for-parameter), Display.teardown] No
    value passed for parameter 'self' in function call

It's very odd because the function call in stbt.py:1680 is:

    elem.send_event(Gst.Event.new_eos())

And Gst.Event should be ignored by pylint due to the "ignored-classes"
configuration in extra/pylint.conf.