Fix display information.

lib/units/device/plugins/service.js

@@ -345,6 +345,10 @@ module.exports = syrup.serial()
             , density: response.density
             , rotation: response.rotation
             , secure: response.secure
+            , size: Math.sqrt(
+                Math.pow(response.width / response.xdpi, 2) +
+                Math.pow(response.height / response.ydpi, 2)
+              )
             }
           }
           throw new Error('Unable to retrieve display information')