Merge pull request OAI#1013 from ePaul/patch-2

add missing ":" and quotes in callback object example

Author: webron

versions/3.0.md

@@ -1847,12 +1847,12 @@ myWebhook:
       requestBody:
         description: Callback payload
         content: 
-          'application/json'
+          'application/json':
             schema:
               $ref: '#/components/schemas/SomePayload'
       responses:
         '200':
-          description: webhook successfully processed an no retries will be performed
+          description: webhook successfully processed and no retries will be performed
 ```