Fixed compatibility issue with pyproj 2.0+

Starting with version 2.0, the `pyproj.pyproj_datadir` constant was deprecated in favor of the `pyproj.datadir.get_data_dir()` constant.
A minor alteration to Basemap's `__init__.py` file allows compatibility with both the newer and older versions of pyproj regarding this breaking change.

Author: pandrey-fr

lib/mpl_toolkits/basemap/__init__.py

@@ -149,7 +149,10 @@
              }
 
 # create dictionary that maps epsg codes to Basemap kwargs.
-epsgf = open(os.path.join(pyproj.pyproj_datadir,'epsg'))
+if hasattr(pyproj, 'datadir'):
+    epsgf = open(os.path.join(pyproj.datadir.get_data_dir(), 'epsg'))
+else:
+    epsgf = open(os.path.join(pyproj.pyproj_datadir, 'epsg'))
 epsg_dict={}
 for line in epsgf:
     if line.startswith("#"):