Fix to work on latest elixir and with defrecord from_lib

This fixes some issues trying to use this on the latest elixir, both with the defined elixir version and with the from_lib call (which would fail when using this as a dependency as it got an `enoent` looking for the file.

Details on a similar problem I found on stack overflow here: http://stackoverflow.com/questions/20160956/elixir-cant-get-to-record-extract-between-2-deps