Merge pull request #397 from mizoguche/set-milestone

Add GHIssue#setMilestone

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

@@ -203,6 +203,10 @@ public class GHIssue extends GHObject implements Reactable{
         edit("body",body);
     }
 
+    public void setMilestone(GHMilestone milestone) throws IOException {
+        edit("milestone",milestone.getNumber());
+    }
+
     public void assignTo(GHUser user) throws IOException {
         setAssignees(user);
     }