GitHub Enterprise does not have a rate limit for whitelisted users

I'm getting the following error with my GitHub Enterprise installation:

```
Error while accessing rate limit API
java.io.FileNotFoundException: http://dsadpcgit2poreh.plaza.ds.adp.com/api/v3/rate_limit
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1401)
	at org.kohsuke.github.Requester.parse(Requester.java:298)
	at org.kohsuke.github.Requester._to(Requester.java:175)
	at org.kohsuke.github.Requester.to(Requester.java:141)
	at org.kohsuke.github.GitHub.getRateLimit(GitHub.java:228)
	at org.jenkinsci.plugins.ghprb.GhprbRepository.checkState(GhprbRepository.java:57)
	at org.jenkinsci.plugins.ghprb.GhprbRepository.check(GhprbRepository.java:77)
	at org.jenkinsci.plugins.ghprb.Ghprb.run(Ghprb.java:72)
	at org.jenkinsci.plugins.ghprb.GhprbTrigger.run(GhprbTrigger.java:181)
	at hudson.triggers.Trigger.checkTriggers(Trigger.java:255)
	at hudson.triggers.Trigger$Cron.doRun(Trigger.java:203)
	at hudson.triggers.SafeTimerTask.run(SafeTimerTask.java:54)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351)
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:165)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:701)
```

The response that I get back from the rate_limit URL is as follows:
HTTP Status Code: 404
Body: 
```json
{
  "message": "No rate limit for white listed users"
}
```

I was going to open a pull request for this myself, but I'm having issues with IntelliJ.  If I can get my issues resolved, I'll take a look at fixing this...