Add a wercker setting for specified config file

[mattstratton]

This will allow us to set BaseURL to localhost for local dev and the proper one in production

See https://github.com/ArjenSchwarz/wercker-step-hugo-build

[mattstratton]

Unsure if this is needed.

[mattstratton]

CLosing this for now because it hasn't been causing issues. Might have been a hugo bug in previous versions.