config: move food-chain to after luhn
config: move food-chain to after luhn

Requested at:
https://github.com/exercism/xgo/pull/398#discussion_r83190972

This was pulled out of that PR and committed separately to master, since
it deserves to be its own commit, but we needed to use squash-and-merge
on #398.

robphoenix/exercism-go,leenipper/xgo,exercism/xgo,exercism/xgo,robphoenix/exercism-go,leenipper/xgo