fixed incorrect ref.child() api, was expecting an array, api should expect a path string that is then split by '/'

Author: Salakar

lib/modules/database/reference.js

@@ -264,8 +264,8 @@ export default class Reference extends ReferenceBase {
     return new Disconnect(this);
   }
 
-  child(...paths: Array<string>) {
-    return new Reference(this.db, this.path.concat(paths));
+  child(path: string) {
+    return new Reference(this.db, this.path.concat(path.split('/')));
   }
 
   toString(): string {