More informative error when using a 0.10 module

If an 0.10 module is used on a 0.11 project, the configuration fails on a `prep` assert that is hard to understand. We can add a better check with a more informative error message, e.g. 

    :duct.module/logging returned a map when we expect a function.
    Perhaps this is an older module, and needs upgrading?