fix incorrect return values for aws-serverless-express proxy (#35131)
fix incorrect return values for aws-serverless-express proxy (#35131)

* fix incorrect return values for aws-serverless-express proxy

proxy() returns a ProxyResult as long as resolutionMode is provided.
https://github.com/awslabs/aws-serverless-express/blob/master/src/index.js#L210

As it is now, the types are misleading and prevent you from awaiting the promise, which is required for it all to work.

* Update aws-serverless-express/index to make unified-signatures pass

https://travis-ci.org/DefinitelyTyped/DefinitelyTyped/builds/526699822#L572

dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped