go.mod: fix jacobsa/crypto build on riscv64

[paralin]

Replace dependency jacobsa/crypto with a fork with support for riscv64.

Issue: https://github.com/rfjakob/gocryptfs/issues/666

Upstream PR: https://github.com/jacobsa/crypto/issues/13

Unaddressed on jacobsa/crypto:

https://github.com/jacobsa/crypto/pull/14#issuecomment-1182744229