Allow lifetime usage in custom_derive! macro

[Nimamoh]

Hello,

I recently tried the custom derive with derive_builder on a lifetimed struct like this:

custom_derive! {
    #[derive(Debug, PartialEq, Default, Clone, Builder)]
    struct Another<'a> {
        title: &'a str,
    }
}

The rust compiler gives me this error:

error�: expected ident, found 'a�