[document-conversion] Fixes conditional statement

Fixes a conditional statement to resolve Travis CI failure.

Author: samir-patel

watson_developer_cloud/document_conversion_v1.py

@@ -39,7 +39,7 @@ def convert_document(self, document, config, media_type=None):
                             accept_json=accept_json)
 
     def index_document(self, config, document=None, metadata=None, media_type=None):
-        if document == None and metadata == None:
+        if document is None and metadata is None:
             raise AssertionError('Missing required parameters: document or metadata. At least one of those is required.')
         params = {'version': self.version}
         files = [('config', ('config.json', json.dumps(config), 'application/json'))]