Default git cl upload to a reasonable server

Replace a Rietveld server that no one controls to Cobalt's public code
review server.

Change-Id: I6d938b402bba0696861e573c59dc0d45b0de6ca9
diff --git a/git_cl.py b/git_cl.py
index 9b6be1e..c172fef 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -57,7 +57,7 @@
 
 __version__ = '1.0'
 
-DEFAULT_SERVER = 'https://codereview.appspot.com'
+DEFAULT_SERVER = 'https://cobalt-review.googlesource.com'
 POSTUPSTREAM_HOOK_PATTERN = '.git/hooks/post-cl-%s'
 DESCRIPTION_BACKUP_FILE = '~/.git_cl_description_backup'
 GIT_INSTRUCTIONS_URL = 'http://code.google.com/p/chromium/wiki/UsingGit'