fix(predictions): use serial queue for WebSocketSession delegate queu… #625

Job	Run time
GraphQL \| User Pool Tests	0s
GraphQL \| Auth Directive Tests	0s
GraphQL \| IAM Tests	0s
GraphQL \| Lazy Load Tests	0s
REST \| User Pool Tests	0s
Functional Tests / API Integration Tests \| Functional (iOS) / iOS Tests \| AWSAPIPluginFunctionalTests	8m 7s
Functional Tests / API Integration Tests \| Functional (tvOS) / tvOS Tests \| AWSAPIPluginFunctionalTests	6m 17s
Functional Tests / API Integration Tests \| Functional (watchOS) / watchOS Tests \| AWSAPIPluginFunctionalTestsWatch	6m 18s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (iOS) / iOS Tests \| AWSAPIPluginGraphQLLambdaAuthTests	6m 24s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (tvOS) / tvOS Tests \| AWSAPIPluginGraphQLLambdaAuthTests	3m 18s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (watchOS) / watchOS Tests \| AWSAPIPluginGraphQLLambdaAuthTestsWatch	4m 57s
REST \| IAM Tests / API Integration Tests \| REST IAM (iOS) / iOS Tests \| AWSAPIPluginRESTIAMTests	4m 52s
REST \| IAM Tests / API Integration Tests \| REST IAM (tvOS) / tvOS Tests \| AWSAPIPluginRESTIAMTests	3m 7s
REST \| IAM Tests / API Integration Tests \| REST IAM (watchOS) / watchOS Tests \| AWSAPIPluginRESTIAMTestsWatch	3m 27s
	46m 47s

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