fix for GH Enterprise which does not have rate limit reset field

Fixes regression from a4c1c8de24

src/main/java/org/kohsuke/github/GitHub.java

@@ -45,6 +45,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
 
 import org.apache.commons.codec.binary.Base64;
 
@@ -248,6 +249,7 @@ public class GitHub {
             // see issue #78
             GHRateLimit r = new GHRateLimit();
             r.limit = r.remaining = 1000000;
+            r.reset = new Date(System.currentTimeMillis() + TimeUnit.HOURS.toMillis(1));
             return r;
         }
     }