Using Miniconda in Travis CI

Replaced calls to apt-get with Miniconda
(http://repo.continuum.io/miniconda/) for the latest scipy and numpy.
Tests were breaking because of the old scipy in Travis (0.9.0).

This was copied from:

* https://gist.github.com/dan-blanchard/7045057
* https://github.com/Jorge-C/ordination/blob/master/.travis.yml
Merge pull request #79 from leouieda/travis-miniconda

Using Miniconda in Travis CI