Show robots.txt on www & domainless only

[ericclemmons]

See this:

evolution/generator-wordpress#8

[AntJanus]

@ericclemmons wasn't this resolved months ago?

[ericclemmons]

For v0.3.0, I'd like this to be something handled outside of the project's .htaccess. Same goes for the H5BP rules, which muck of an otherwise simple WordPress install.