Fix API example

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -17,6 +17,7 @@
 - Fix reverse inheritance permissions.
 - Remove index create permission as an ACL permission
   for indexes.
+- Fix API example.
 
 3.2.10 (2019-11-19)
 ===================

docs/chapters/api.rst

@@ -57,7 +57,7 @@ Get a list of document types::
 
 Upload a new document::
 
-    with open('test_document.pdf', mode='rb') as
+    with open('test_document.pdf', mode='rb') as file_object:
         requests.post('http://127.0.0.1:8000/api/documents/', auth=('username', 'password'), files={'file': file_object}, data={'document_type': 1}).json()
 
     {u'description': u'',