Not implemented for `nickel_postgres::PostgresMiddleware`

[suesslin]

An error occurred, when I tried to utilize my Nickle with a PostgresMiddleware.

^^^^^^^ the trait `for<'r, 'mw, 'conn> std::ops::FnOnce<(&'r mut nickel::Request<'mw, 'conn>, nickel::Response<'mw>)>` is not implemented for `nickel_postgres::PostgresMiddleware`