exclude the "offline" dir in gh-pages?

[xuwei-k]

• https://github.com/foundweekends/giter8/tree/gh-pages/offline
• http://www.foundweekends.org/giter8/offline/
• https://github.com/foundweekends/pamflet/commit/ca86addf0f7c62bc728cbe4aea1ecc608eb2ea84

I thinks the "offline" dir is unnecessary. I have excluded in pamflet but I'm not sure this is best way https://github.com/foundweekends/pamflet/blob/7bde909caa1e19f9d9abdd15b6f76a436c1b7830/build.sbt#L57-L63

[eed3si9n]

That was created for html5 offline cache to read the docs offline. Not sure if it's needed.