Change default IP

Makes https://github.com/middleman/middleman/pull/1248 actually work...
Was sure I tested this and it worked but then I was on an older version of middleman.

I believe the `||` operator here https://github.com/Arcovion/middleman/commit/e3946a06d911fa24159e136b5b526c97d4e71d21 will still be needed for those who just want to use `middleman-core` and not the CLI stuff