Tweaked update_version.py to leave PHP notes blank

Until now update_version.py has copied the notes from the previous PHP
release, which is not very useful.

update_version.py

diff --git a/update_version.py b/update_version.py
index bfbef45..470e425 100755
--- a/update_version.py
+++ b/update_version.py
@@ -317,7 +317,7 @@
           FindAndClone(root, 'date'),
           FindAndClone(root, 'time'),
           FindAndClone(root, 'license'),
-          FindAndClone(root, 'notes')
+          CreateNode('notes', 3, []),
         ])
       changelog.appendChild(release)
       changelog.appendChild(document.createTextNode('\n '))