Fix docstring for PretrainedBertIndexer's pretrained_model param
`pretrained_model` is not an optional param, as stated in `PretrainedBertIndexer` docs, so I removed the "optional" part from it.
@@ -201,7 +201,7 @@ class PretrainedBertIndexer(WordpieceIndexer):
Parameters
----------
- pretrained_model: ``str``, optional (default = None)
+ pretrained_model: ``str``
Either the name of the pretrained model to use (e.g. 'bert-base-uncased'),
or the path to the .txt file with its vocabulary.
