sync: Keep the project.list file sorted

Its easier to locate an entry visually if the file is sorted.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 6bccbb0..bd07dd9 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -166,6 +166,7 @@
                 break
               dir = os.path.dirname(dir)
 
+    new_project_paths.sort()
     fd = open(file_path, 'w')
     try:
       fd.write('\n'.join(new_project_paths))