fix getInstance of CoreStoreSembastImp (#438)

Author: fischerscode

lib/parse_server_sdk.dart

@@ -135,8 +135,7 @@ class CoreStoreSembastImp implements sdk.CoreStoreSembastImp {
 
   static sdk.CoreStoreSembastImp _sembastImp;
 
-  static Future<sdk.CoreStore> getInstance(String dbPath,
-      {DatabaseFactory factory, String password}) async {
+  static Future<sdk.CoreStore> getInstance({DatabaseFactory factory, String password}) async {
     if (_sembastImp == null) {
       String dbDirectory = '';
       if (!sdk.parseIsWeb &&