chore(package): update clean-css to version 3.4.11
chore(package): update clean-css to version 3.4.11

http://greenkeeper.io/
Jenselme/ngeo,camptocamp/ngeo,ger-benjamin/ngeo,adube/ngeo,camptocamp/ngeo,ger-benjamin/ngeo,ger-benjamin/ngeo,pgiraud/ngeo,camptocamp/ngeo,Jenselme/ngeo,kalbermattenm/ngeo,camptocamp/ngeo,adube/ngeo,Jenselme/ngeo,pgiraud/ngeo,adube/ngeo,kalbermattenm/ngeo,adube/ngeo,pgiraud/ngeo,Jenselme/ngeo,camptocamp/ngeo,kalbermattenm/ngeo