Fix to_yaml silliness

roles/matrix-server/templates/synapse/homeserver.yaml.j2

@@ -96,7 +96,7 @@ public_baseurl: https://{{ hostname_matrix }}/
 soft_file_limit: 0
 
 # Set to false to disable presence tracking on this homeserver.
-use_presence: {{ matrix_synapse_use_presence|to_yaml }}
+use_presence: {{ matrix_synapse_use_presence|to_json }}
 
 # The GC threshold parameters to pass to `gc.set_threshold`, if defined
 # gc_thresholds: [700, 10, 10]