chore(package): update phantomjs-prebuilt to version 2.1.6
chore(package): update phantomjs-prebuilt to version 2.1.6

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