mkcert -install (v1.4.0) fails to run in Ubuntu 16.04: SEC_ERROR_READ_ONLY

Ubuntu 16.04, linuxbrew-installed mkcert v1.4.0, mkcert -install fails with certutil error:

```
mkcert -install
Created a new local CA at "/home/circleci/.local/share/mkcert" 💥
The local CA is now installed in the system trust store! ⚡️
ERROR: failed to execute "certutil -A": exit status 255

certutil: function failed: SEC_ERROR_READ_ONLY: security library: read-only database.
```