Colon typo in source/user_manual.rst

[far-authentise]

Typo in source/user_manual.rst at example with paragraph before it starting with ' The data provided will be included the recipients email via a header called X-Mailgun-Variables.' in the last_name value

As-is (note last_name):

     {
         "event": "delivered",
         "user-variables": {
             "first_name": "John",
             "last_name:" "Smith",
             "my_message_id": "123"
         }
     }

Corrected: (note last_name):

     {
         "event": "delivered",
         "user-variables": {
             "first_name": "John",
             "last_name": "Smith",
             "my_message_id": "123"
         }
     }

[zeefarmer]

Fixed in https://github.com/mailgun/documentation/pull/639