fix for 'TypeError: Object #<ServerResponse> has no method 'type' error'

Running Express 2.X, when setting the 'type' option for a given cached route would cause this runtime error:

TypeError: Object #<ServerResponse> has no method 'type'
    at Object.handle (/Users/giorgiog/Projects/Virtuoso/maestro/server/output/node_modules/express-view-cache/index.js:32:22)

Rather than setting response.__type__ (which doesn't seem to exist), I simply call response.setHeader...