Fix sample config

Just a small change missed in 7950aa8.

docs/sample_config.yaml

@@ -2232,7 +2232,7 @@ ui_auth:
     # session to be active.
     #
     # This defaults to 0, meaning the user is queried for their credentials
-    # before every action, but this can be overridden to alow a single
+    # before every action, but this can be overridden to allow a single
     # validation to be re-used.  This weakens the protections afforded by
     # the user-interactive authentication process, by allowing for multiple
     # (and potentially different) operations to use the same validation session.