Workaround npm registry bug by downloading windshaft from github
Workaround npm registry bug by downloading windshaft from github

See the problem here:
https://travis-ci.org/CartoDB/Windshaft-cartodb/builds/18663972

UCL-ShippingGroup/Windshaft-cartodb,manueltimita/Windshaft-cartodb,CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,manueltimita/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,CartoDB/Windshaft-cartodb,manueltimita/Windshaft-cartodb,CartoDB/Windshaft-cartodb