Magento – Magento 2.0.X Authorize.net Direct Post keeps on showing loading after clicking place order

I am working for Magento 2 right from its first version. Till now for payments i have used only Paypal Express Checkout. But now there is requirement to integrate Authorize.net direct post. And i have tried to integrate it using sandbox credentials.

Now when i am on checkout page selecting Authorize.net to make payments by using sandbox sample card number e.g. : – American Express Test Card: 370000000000002 , When i click on place order it keeps on showing loader. But if i can see in admin panel under Sales > Order m It shows the order that i have just placed.

I have searched allot and found some people have posted the same issue , but they have also mentioned the PHP version as 7.0.x where they are getting issue.
e.g here

But i am using PHP Version 5.6.20 and also I have got this issue first with Magento 2.0.6 version. Now i have done fresh Magento 2.0.7 installation on new server, but the issues is still there

My admin panel configuration settings for Authorize.net are

Test Mode : Yes

Gateway Url : https://secure.authorize.net/gateway/transact.dll

I have even tried with

https://test.authorize.net/gateway/transact.dll

Transaction Details Url : https://api2.authorize.net/xml/v1/request.api

Debug : Yes

Now when i have checked debug.log

it is saying

[2016-05-27 12:35:03] main.DEBUG: cache_invalidate:  {"method":"POST","url":"http://example.com/authorizenet/directpost_payment/place/","invalidateInfo":{"tags":["catalog_category_3","catalog_category"],"mode":"matchingAnyTag"},"is_exception":false} []
[2016-05-27 12:35:03] main.DEBUG: array (
  'request' => 
  array (
    'x_version' => '3.1',
    'x_delim_data' => 'FALSE',
    'x_relay_response' => 'TRUE',
    'x_test_request' => 'TRUE',
    'x_login' => '****',
    'x_method' => 'CC',
    'x_relay_url' => http://example.com/authorizenet/directpost_payment/response',
    'x_type' => 'AUTH_CAPTURE',
    'x_fp_sequence' => '2',
    'x_invoice_num' => '000000002',
    'x_amount' => 5.0099999999999998,
    'x_currency_code' => 'USD',
    'x_tax' => '0.00',
    'x_freight' => '5.00',
    'x_first_name' => 'Dinesh',
    'x_last_name' => 'Saini',
    'x_company' => '',
    'x_address' => 'test',
    'x_city' => 'California',
    'x_state' => 'Alabama',
    'x_zip' => '90001',
    'x_country' => '',
    'x_phone' => '1234567890',
    'x_fax' => '',
    'x_cust_id' => '',
    'x_customer_ip' => '122.173.244.114',
    'x_customer_tax_id' => '',
    'x_email' => 'dineshs@test.com',
    'x_email_customer' => '1',
    'x_merchant_email' => '',
    'x_ship_to_first_name' => 'Dinesh',
    'x_ship_to_last_name' => 'Saini',
    'x_ship_to_company' => '',
    'x_ship_to_address' => 'test',
    'x_ship_to_city' => 'California',
    'x_ship_to_state' => 'Alabama',
    'x_ship_to_zip' => '90001',
    'x_ship_to_country' => '',
    'x_po_num' => '',
    'x_fp_timestamp' => 1464352503,
    'x_fp_hash' => '27827498413496cd9ad6ed247e9688f3',
  ),
) {"is_exception":false} []

Can anyone please help , is there anything wrong in my configuration or i have tried with something else.