gclient: update logging.warn to logging.warning.

logging.warn is deprecated.

Change-Id: I047f356b8eeced631edc51e3b846f0995f4ce95e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2124526
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
diff --git a/gclient.py b/gclient.py
index d132d3c..285bb01 100755
--- a/gclient.py
+++ b/gclient.py
@@ -601,7 +601,7 @@
               self.url))
       # In theory we could keep it as a shadow of the other one. In
       # practice, simply ignore it.
-      logging.warn('Won\'t process duplicate dependency %s' % sibling)
+      logging.warning("Won't process duplicate dependency %s" % sibling)
       return False
     return True