COMPAT: fwd and bkwd compatibility with fiona CRS (#913)

Background: Toblerity/Fiona#714.

geopandas/io/file.py

@@ -75,7 +75,15 @@ def read_file(filename, bbox=None, **kwargs):
 
     with fiona_env():
         with reader(path_or_bytes, **kwargs) as features:
-            crs = features.crs
+
+            # In a future Fiona release the crs attribute of features will
+            # no longer be a dict. The following code will be both forward
+            # and backward compatible.
+            if hasattr(features.crs, 'to_dict'):
+                crs = features.crs.to_dict()
+            else:
+                crs = features.crs
+
             if bbox is not None:
                 if isinstance(bbox, GeoDataFrame) or isinstance(bbox, GeoSeries):
                     bbox = tuple(bbox.to_crs(crs).total_bounds)