matrix: Configure a bad word

If the protection is enabled, saying any of these words shortly after
joining triggers a ban.

roles/matrix/templates/mjolnir.yaml.j2

@@ -114,7 +114,8 @@ protections:
     # A list of words which should be monitored by the bot.  These will match if any part
     # of the word is present in the message in any case.  e.g. "hello" also matches
     # "HEllO".  Additionally, regular expressions can be used.
-    words: []
+    words:
+        - "nigger"
 
     # How long after a user joins the server should the bot monitor their messages.  After
     # this time, users can say words from the wordlist without being banned automatically.