Extend usage to restify

[willfarrell]

when using restify; res.contentType generates:

{ [TypeError: res.contentType is not a function]
  domain: 
   Domain {
     domain: null,
     _events: { error: [Function] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] },
  domainThrown: true }