fix for netCDF4 v1.7.3 iterator changes

Author: kafitzgerald

src/wrf/util.py

@@ -134,7 +134,13 @@ def is_multi_file(wrfin):
         is a single NetCDF file object.
 
     """
-    return (isinstance(wrfin, Iterable) and not isstr(wrfin))
+    try:
+        iter(wrfin)
+        is_iterable = True
+    except Exception:
+        is_iterable = False
+
+    return (is_iterable and not isstr(wrfin))
 
 
 def has_time_coord(wrfnc):