BLD: Fixed calculation of pip cache directory on travis
BLD: Fixed calculation of pip cache directory on travis

alphaBenj/zipline,bartosh/zipline,humdings/zipline,enigmampc/catalyst,wilsonkichoi/zipline,bartosh/zipline,wilsonkichoi/zipline,quantopian/zipline,umuzungu/zipline,florentchandelier/zipline,alphaBenj/zipline,humdings/zipline,Scapogo/zipline,florentchandelier/zipline,magne-max/zipline-ja,quantopian/zipline,magne-max/zipline-ja,Scapogo/zipline,enigmampc/catalyst,umuzungu/zipline