doc: Update serverless minimum requirement (#451)

Author: ankon

README.md

@@ -15,7 +15,7 @@ Be sure to check out all that [AWS AppSync](https://aws.amazon.com/appsync) has
 # Minimum requirements
 
 - [Node.js v8 or higher](https://nodejs.org)
-- [Serverless v1.30.0 or higher](https://github.com/serverless/serverless)
+- [Serverless v1.83.3 or higher](https://github.com/serverless/serverless)
 
 # Installation & Configuration