changed visualgrep link

Author: dafi

_config.yml

@@ -48,7 +48,7 @@ navigation_links:
      - title: VisualDiffer
        link: *official_link
      - title: VisualGrep
-       link: http://visualgrep.com
+       link: https://itunes.apple.com/us/app/visualgrep/id597887722?mt=12
      - title: Clipboard Plain
        link: https://itunes.apple.com/us/app/clipboardplain/id528607880?mt=12