Update git cl try command to mention tryserver.chromium.linux.

This is a purely cosmetic CL.

R=agable@chromium.org
BUG=395196

Review URL: https://codereview.chromium.org/415903002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@286230 0039d316-1c4b-4281-b951-d872f2087c98

git_cl.py

@@ -2277,7 +2277,7 @@ def CMDtry(parser, args):
 
   if options.bot and not options.master:
     parser.error('For manually specified bots please also specify the '
-                 'tryserver master, e.g. "-m tryserver.chromium".')
+                 'tryserver master, e.g. "-m tryserver.chromium.linux".')
 
   def GetMasterMap():
     # Process --bot and --testfilter.