TST: Increase the timeout on the Travis pip install

H/T to @ogrisel for suggesting this:
https://github.com/nipy/dipy/pull/474/files#r20766386
Merge pull request #478 from arokem/travis-time

TST: Increase the timeout on the Travis pip install

H/T to @ogrisel for suggesting this:
https://github.com/nipy/dipy/pull/474/files#r20766386