edit added 3-rd party package link (#3969)

There was a problem with the GitHub package link that was fixed

README.rst

 .. _`CyberSource Secure Acceptance Silent Order Post`: https://www.cybersource.com/products/payment_security/secure_acceptance_silent_order_post/
 .. _django-oscar-wfrs: https://github.com/thelabnyc/django-oscar-wfrs
 .. _`Wells Fargo Retail Services`: https://retailservices.wellsfargo.com/
-.. _django-oscar-zarinpal-gateway:https://github.com/mojtabaakbari221b/django-oscar-zarinpal-gateway
+.. _django-oscar-zarinpal-gateway: https://github.com/mojtabaakbari221b/django-oscar-zarinpal-gateway
+
 
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