Fix event listener method for content opacity (#907)

Author: willum070

samples/advanced-markers-animation/index.ts

@@ -87,7 +87,7 @@
     });
 
     content.style.opacity = '0'; 
-    content.addEventListener('animationend', (event) => { 
+    content.addListener('animationend', (event) => { 
       content.classList.remove('drop');
       content.style.opacity = '1';
     });
@@ -108,4 +108,4 @@
   }
 
 initMap();
-// [END maps_advanced_markers_animation]
+// [END maps_advanced_markers_animation]