The >= syntax is deprecated. Putting the line as the first line in the
file is not strictly necessary for 1.16, but it is allegedly necessary
as of 2.2 and harmless before then.

https://cabal.readthedocs.io/en/stable/cabal-package-description-file.html#pkg-field-cabal-version

This also requires updating dependencies to use crypton.

Unfortunately, cryptostore will only use crypton if the use_crypton
Cabal flag is enabled, and we can't make that happen from our cabal
file. I opened an issue to ask them to remove `manual: True` from their
flag, so that the solver can try enabling it. See:
ocheron/cryptostore#13