bert align_bert_tokens_to_corpus_tokens fails with Pandas 1.2.0

[BryanCutler]

bert.align_bert_tokens_to_corpus_tokens() fails with Pandas 1.2.0 due to the error described here:

#157 (comment)

[frreiss]

Note: We currently have a workaround in place for this problem, but the workaround involves monkey-patching parts of Pandas' __repr__.

[BryanCutler]

This was actually due to an error aggregation on extension arrays which I fixed upstream at pandas-dev/pandas#38982 and is in v1.2.1. We can close this now.