Fix comment

Author: duckduckgrayduck

documentcloud/documents.py

@@ -349,7 +349,7 @@ def _extract_ocr_options(self, kwargs):
 
         Returns:
             force_ocr (bool)
-            ocr_engine (str or None)
+            ocr_engine (str)
         """
         force_ocr = kwargs.pop("force_ocr", False)
         ocr_engine = kwargs.pop("ocr_engine", "tess4")