Change WOFF MIME type to `application/font-woff`

The WOFF MIME Type was formally registered as `application/font-woff`:
http://www.iana.org/assignments/media-types/application/font-woff

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@josh also, recently [WOFF 2.0](http://www.w3.org/TR/WOFF2/) was introduced, but [there isn't yet an recommended file extension and MIME type](https://github.com/h5bp/server-configs-apache/issues/32#issuecomment-46683006) for it.