fix(DataStore): Add 'weak self' to prevent retain cycles in OutgoingM… #337

Job	Run time
GraphQL \| Auth Directive Tests	0s
GraphQL \| IAM Tests	0s
GraphQL \| Lazy Load Tests	0s
GraphQL \| User Pool Tests	0s
REST \| User Pool Tests	0s
Functional Tests / API Integration Tests \| Functional (iOS) / iOS Tests \| AWSAPIPluginFunctionalTests	18m 2s
Functional Tests / API Integration Tests \| Functional (tvOS) / tvOS Tests \| AWSAPIPluginFunctionalTests	13m 24s
Functional Tests / API Integration Tests \| Functional (watchOS) / watchOS Tests \| AWSAPIPluginFunctionalTestsWatch	16m 35s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (iOS) / iOS Tests \| AWSAPIPluginGraphQLLambdaAuthTests	13m 42s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (watchOS) / watchOS Tests \| AWSAPIPluginGraphQLLambdaAuthTestsWatch	7m 14s
REST \| IAM Tests / API Integration Tests \| REST IAM (iOS) / iOS Tests \| AWSAPIPluginRESTIAMTests	9m 2s
GraphQL \| Lambda Tests / API Integration Tests \| GraphQL Lambda (tvOS) / tvOS Tests \| AWSAPIPluginGraphQLLambdaAuthTests	8m 23s
REST \| IAM Tests / API Integration Tests \| REST IAM (tvOS) / tvOS Tests \| AWSAPIPluginRESTIAMTests	9m 55s
REST \| IAM Tests / API Integration Tests \| REST IAM (watchOS) / watchOS Tests \| AWSAPIPluginRESTIAMTestsWatch	8m 29s
	1h 44m 46s

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