turn on pip caching for travis
turn on pip caching for travis

mlhenderson/data_api,kkellerlbl/data_api,kbase/data_api,kbase/data_api,mlhenderson/data_api,realmarcin/data_api,mlhenderson/data_api,kkellerlbl/data_api,kbase/data_api,kkellerlbl/data_api,mlhenderson/data_api,kkellerlbl/data_api,kkellerlbl/data_api,mlhenderson/data_api,kbase/data_api,kbase/data_api