Your Certbot version is too old relative to your cryptography library, which probably is more recent than version 2.1.
In cryptography version >2.1 the verifier() function was removed and in Remove use of deprecated verifier with cryptography (#9105) · certbot/certbot@267fb94 · GitHub Certbot fixed this. However, that fix was not present in version 1.21.0 of Certbot, but since version 1.22.0.
So you either need to update your Certbot to 1.22.0 or newer or downgrade your cryptography library to version 2.1 or older.