Use git to get whipper's version

This essentially a copy of code from spotify2musicbrainz:
59157165c4

Given that that code is in GPLv3 (and I'm its author :)), it should be
fine to use. It is mostly boilerplate from upstream documentation
anyway: https://pypi.org/project/setuptools-scm/

Should fix https://github.com/whipper-team/whipper/issues/337

Signed-off-by: Frederik “Freso” S. Olesen <freso.dk@gmail.com>

.travis.yml

@@ -11,7 +11,7 @@ install:
     - sudo apt-get -qq update
     - sudo pip install --upgrade -qq pip
     - sudo apt-get -qq install cdparanoia cdrdao flac gir1.2-glib-2.0 libcdio-dev libiso9660-dev libsndfile1-dev python-cddb python-gi python-musicbrainzngs python-mutagen python-setuptools sox swig libcdio-utils
-    - sudo pip install pycdio==0.21 requests
+    - sudo pip install pycdio==0.21 requests setuptools_scm
 
     # Testing dependencies
     - sudo apt-get -qq install python-twisted-core