Fix typo

Author: junichi11

src/main/java/com/junichi11/netbeans/modules/github/issues/issue/ui/AttributesViewPanel.java

@@ -101,7 +101,7 @@ public void setAttributes(Issue issue, GitHubRepository repository) {
         if (milestone != null) {
             milestoneNameLabel.setText(milestone.getTitle());
 
-            // tooptip
+            // tooltip
             Date dueDate = milestone.getDueOn();
             String description = milestone.getDescription();
             StringBuilder sb = new StringBuilder();