Fix unassigned tf_contrib_err issue (#58)

Author: markurtz

src/sparseml/tensorflow_v1/utils/variable.py

@@ -20,6 +20,7 @@
 try:
     import tensorflow.contrib.graph_editor as graph_editor
     from tensorflow.contrib.graph_editor.util import ListView
+    tf_contrib_err = None
 except Exception as err:
     graph_editor = None
     ListView = None