Fix occasional BERT sentence length warning

[freddyheppell]

UserWarning: some of your sentences have more tokens than "max_seq_len=25" set on the server, as consequence you may get less-accurate or truncated embeddings.
here is what you can do:
- disable the length-check by create a new "BertClient(check_length=False)" when you do not want to display this warning
- or, start a new server with a larger "max_seq_len"
  warnings.warn('some of your sentences have more tokens than "max_seq_len=%d" set on the server, '