Migrate from Gensim 3 to Gensim 4

[koaning]

There's a guide here: https://github.com/RaRe-Technologies/gensim/wiki/Migrating-from-Gensim-3.x-to-4

[koaning]

I've frozen the gensim version to 3 for now https://github.com/RasaHQ/rasa-nlu-examples/pulls. We should upgrade to 4 at some point. It's probably best to delay this until some of our users start to notice. Not everyone has transitioned to version 4 just yet.

[koaning]

We may need to double-check if we support gensim 4.0 now bheinzerling/bpemb#56 in relation to bpemb.