Roles permissions are not mixed correctly

[b3ni]

// permissions based on role.
// more permissive permission wins
// if user has multiple roles we keep
// true values.

This does not happen because of the following condition:

if( !array_key_exists( $clearance, $permissions[$slug] ) ) {
! $value ?: $permissions[$slug][$clearance] = true;
}

[QuentinPetel]

See #169.