Fixed flippable doctest.

dist/iwmlib.pixi.js

@@ -5805,6 +5805,7 @@
          * @param {object} [opts] - An options object. See the hammer documentation for more details.
          */
         static on(types, elements, cb, opts = {}) {
+            
             opts = Object.assign({}, {
 
             }, opts);
@@ -7615,7 +7616,6 @@
             /* Buttons are not guaranteed to exist. */
             if (this.infoBtn) {
                 InteractionMapper$1.on('tap', this.infoBtn, event => this.flip.start());
-
                 this.enable(this.infoBtn);
             }
             if (this.backBtn) {