travis: make sure pypy is installed
travis: make sure pypy is installed

iksaif/biggraphite,Thib17/biggraphite,criteo/biggraphite,dpanth3r/biggraphite,Thib17/biggraphite,criteo/biggraphite,criteo/biggraphite,iksaif/biggraphite,iksaif/biggraphite,Thib17/biggraphite,iksaif/biggraphite,criteo/biggraphite,Thib17/biggraphite