TravisCI: Use pip cache
TravisCI: Use pip cache

shadowoneau/skylines,TobiasLohner/SkyLines,RBE-Avionik/skylines,TobiasLohner/SkyLines,TobiasLohner/SkyLines,Harry-R/skylines,shadowoneau/skylines,shadowoneau/skylines,snip/skylines,Turbo87/skylines,Turbo87/skylines,shadowoneau/skylines,kerel-fs/skylines,kerel-fs/skylines,skylines-project/skylines,snip/skylines,RBE-Avionik/skylines,Turbo87/skylines,Turbo87/skylines,snip/skylines,skylines-project/skylines,Harry-R/skylines,skylines-project/skylines,Harry-R/skylines,RBE-Avionik/skylines,kerel-fs/skylines,skylines-project/skylines,Harry-R/skylines,RBE-Avionik/skylines