news: fix spelling of tunneled

s/tunnelled/tunneled/ in news for the libxl tunneled migration feature.

docs/news.xml

@@ -55,10 +55,10 @@
       </change>
       <change>
         <summary>
-          libxl: add tunnelled migration support
+          libxl: add tunneled migration support
         </summary>
         <description>
-          Add tunnelled migration to libxl driver, which is always capable of
+          Add tunneled migration to libxl driver, which is always capable of
           strong encryption and doesn't require any extra network connection
           other than what's required for remote access of libvirtd.
         </description>