Fix for plugin description file cast error

By: stevenh <steven.hartland@multiplay.co.uk>

paper-api/src/main/java/org/bukkit/plugin/PluginDescriptionFile.java

@@ -85,9 +85,9 @@ public final class PluginDescriptionFile {
     }
 
     private void loadMap(Map<String, Object> map) throws ClassCastException {
-        name = (String)map.get("name");
-        main = (String)map.get("main");
-        version = (String)map.get("version");
+        name = map.get("name").toString();
+        main = map.get("main").toString();
+        version = map.get("version").toString();
     }
 
     private Map<String, Object> saveMap() {