Helpful cast if port is configured as string

If someone makes the stupid mistake of setting the port as a string, e.g. `"4222"` instead of `4222` the live-reload port will be number-string concatenation, resulting in an attempt to connect to e.g. `422231529` instead of `35751` (4200+31529). I did this silly mistake, and thought we'd save others the trouble.

    {
      /**
        Ember CLI sends analytics information by default. The data is completely
        anonymous, but there are times when you might want to disable this behavior.

        Setting `disableAnalytics` to true will prevent any data from being sent.
      */
      "disableAnalytics": false,
      "port": "4200" // silly mistake
    }