TST: Add Pandas 0.17.0rc1 to travis test

Author: David Stephens

.travis.yml

@@ -7,6 +7,7 @@ env:
   - PYTHON=2.7 PANDAS=0.15.1
   - PYTHON=3.3 PANDAS=0.14.1
   - PYTHON=3.4 PANDAS=0.16.2
+  - PYTHON=3.4 PANDAS=0.17.0rc1
   - PYTHON=2.7 PANDAS=0.12.0
   - PYTHON=2.7 PANDAS=0.11.0
   - PYTHON=2.7 PANDAS=0.10.1