Cache pip requirements on Travis (#15)
Cache pip requirements on Travis (#15)

https://docs.travis-ci.com/user/caching/
jcpeterson/Dallinger,Dallinger/Dallinger,jcpeterson/Dallinger,Dallinger/Dallinger,Dallinger/Dallinger,Dallinger/Dallinger,jcpeterson/Dallinger,jcpeterson/Dallinger,jcpeterson/Dallinger,Dallinger/Dallinger