test(GridLayer): fix graphical browser zoom in
test(GridLayer): fix graphical browser zoom in

test on number of pruned tiles during zoom-in in "graphical browsers" (i.e. not PhantomJS) was failing due to missing some rAF to let the animation process fully go through and be able to prune the remaining 4 tiles.

stefanocudini/Leaflet,stefanocudini/Leaflet,Leaflet/Leaflet,CapeSepias/Leaflet,CapeSepias/Leaflet,Leaflet/Leaflet,CapeSepias/Leaflet,Leaflet/Leaflet,stefanocudini/Leaflet