fix: changed custom content type to HashMap<String, Object>

src/main/java/uulm/teamname/marvelous/gamelibrary/events/CustomEvent.java

@@ -1,7 +1,9 @@
 package uulm.teamname.marvelous.gamelibrary.events;
 
+import java.util.HashMap;
+
 /** Represents a custom event ({@link EventType#CustomEvent}). */
 public class CustomEvent extends Event {
     public String teamIdentifier;
-    public Object customContent;
+    public HashMap<String, Object> customContent;
 }