Extra "extensions" property in tag externalDocs

[Helen Kosova]

http://oai.swagger.io/api/convert?url=http://petstore.swagger.io/v2/swagger.json

If a global tag has externalDocs, the converted spec gets an extra property extensions:

"tags": [{
		"name": "pet",
		"description": "Everything about your Pets",
		"externalDocs": {
			"description": "Find out more",
			"url": "http://swagger.io",
			"extensions": {}  <---
		}
	}, {
		"name": "store",
		"description": "Access to Petstore orders"
	}, {
		"name": "user",
		"description": "Operations about user",
		"externalDocs": {
			"description": "Find out more about our store",
			"url": "http://swagger.io",
			"extensions": {}  <---
		}
	}
],

[Ron]

Fixed!