Chat21 is not working on safari browser


![Screen Shot 2019-12-06 at 10 33 29 AM](https://user-images.githubusercontent.com/34370313/70297504-5b654f00-1814-11ea-8349-22f050c6634f.png)


I am getting below Error:
Uncaught (in promise): FirebaseError: Messaging: This browser doesn't support the API's required to use the firebase SDK. (messaging/unsupported-browser). 

Thanks in advanced!!