Update to Leaflet 1 tutorial

We have an updated example for our Leaflet 1 tutorial thanks to some incentive from Matthew McKenna. Leaflet has undergone many changes recently, which rendered our original tutorials obsolete. We are currently restructuring with the 0.6 upgrade (0.6.4 more specifically). Check out the new Setup and Basemap tutorial.

See a complete example of establishing a basemap using Leaflet at Matt’s Github repository: https://github.com/mpmckenna8/leaflettuts