Set fields property of schema resource.

Author: tswast

bigquery/google/cloud/bigquery/table.py

@@ -928,7 +928,9 @@ def upload_from_file(self,
 
         if len(self._schema) > 0:
             load_config = metadata['configuration']['load']
-            load_config['schema'] = _build_schema_resource(self._schema)
+            load_config['schema'] = {
+                'fields': _build_schema_resource(self._schema)
+            }
 
         _configure_job_metadata(metadata, allow_jagged_rows,
                                 allow_quoted_newlines, create_disposition,