speed up travis builds with containers and wheel caching
speed up travis builds with containers and wheel caching

ozak/geopandas,geopandas/geopandas,micahcochran/geopandas,jorisvandenbossche/geopandas,urschrei/geopandas,geopandas/geopandas,jdmcbr/geopandas,ozak/geopandas,micahcochran/geopandas,jorisvandenbossche/geopandas,IamJeffG/geopandas,jorisvandenbossche/geopandas,geopandas/geopandas,jdmcbr/geopandas