Use Login keychain instead of System keychain for truststore_darwin

[s3i7h]

mkcert/truststore_darwin.go

Line 53 in 1c1dc4e

cmd := commandWithSudo("security", "add-trusted-cert", "-d", "-k", "/Library/Keychains/System.keychain", filepath.Join(m.CAROOT, rootName))

mkcert is for development use, and trusting the root CA systemwide is granting too much IMO. Adding it to the per-user Login keychain is sufficient.