fix typo webhok -> webhook

README.md

@@ -91,7 +91,7 @@ zebra_webhook_recurring_payment_succeeded.connect(update_last_invoice_date)
 
 ### Webhooks Update ###
 
-Stripe recently updated their webhok implementation (see https://stripe.com/blog/webhooks). Zebra includes an implementation of the new system.
+Stripe recently updated their webhook implementation (see https://stripe.com/blog/webhooks). Zebra includes an implementation of the new system.
 
 * Include the zebra urls
 * Update your stripe account to point to your webhook URL (aka https://www.mysite.com/zebra/webhooks/v2/)