add Entity.passengers and Entity.vehicle (#75)

Author: qwqtoday

index.d.ts

@@ -44,6 +44,8 @@ declare module 'prismarine-entity' {
         elytraFlying?: boolean
         player?: object;
         effects: Effect[];
+        vehicle: Entity;
+        passengers: Entity[];
         setEquipment(index: number, item: Item): void;
         getCustomName(): ChatMessage | null;
         getDroppedItem(): Item | null;

index.js

@@ -21,6 +21,8 @@ module.exports = (registryOrVersion) => {
       this.equipment = new Array(5)
       this.isValid = true
       this.metadata = []
+      this.passengers = []
+      this.vehicle = null
     }
 
     get mobType () {