Fix rasterio deprecation warnings
Fix rasterio deprecation warnings

See https://github.com/mapbox/rasterio/issues/86 for reference.
Fixes a couple hundred deprecation warnings that come up during testing.

bearecinos/oggm,juliaeis/oggm,anoukvlug/oggm,OGGM/oggm,TimoRoth/oggm,TimoRoth/oggm,bearecinos/oggm,juliaeis/oggm,anoukvlug/oggm,OGGM/oggm