fix env version attribute

httpie/config.py

@@ -104,7 +104,7 @@ class Config(BaseConfigDict):
         try:
             implicit_content_type = self.pop('implicit_content_type')
         except KeyError:
-            pass
+            self.save()
         else:
             if implicit_content_type == 'form':
                 self['default_options'].insert(0, '--form')