Fix config validation to accept new keymap format

Commit I0cd0884e0e1f4f0fa82f93e5f7438ff00c5a992aadded support for
sequences of keys input but config file validation was not updated to
reflect the change.

Change-Id: I9c648686737262148a16d3228413da5939677000

gertty/config.py

@@ -98,7 +98,7 @@ class ConfigSchema(object):
                            'reverse': bool}
 
     keymap = {v.Required('name'): str,
-              v.Match('(?!name)'): v.Any([str], str)}
+              v.Match('(?!name)'): v.Any([[str], str], [str], str)}
 
     keymaps = [keymap]