go get github.com/ProtonMail/go-crypto
This module is backwards compatible with x/crypto/openpgp,
so you can simply replace all imports of golang.org/x/crypto/openpgp with
github.com/ProtonMail/go-crypto/openpgp.
A partial list of changes is here: #21 (comment).
For the more extended API for reading and writing OpenPGP messages use github.com/ProtonMail/go-crypto/openpgp/v2, but it is not fully backwards compatible with golang.org/x/crypto/openpgp.