fix incorrect type

[jpgrusling]

Based on the documentation at https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-verify-auth-challenge-response.html#cognito-user-pools-lambda-trigger-syntax-verify-auth-challenge, the current type is incorrect. This fixes and local testing confirms resolution.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[normj]

Agreed the ChallengeAnswer was mismodeled. Could you update this test JSON file

aws-lambda-dotnet/Libraries/test/EventsTests.Shared/cognito-verifyauthchallenge-event.json

Line 20 in ca6614f

"challengeAnswer": {

and then this test case

aws-lambda-dotnet/Libraries/test/EventsTests.Shared/EventTests.cs

Line 731 in ca6614f

Assert.Equal(2, cognitoVerifyAuthChallengeEvent.Request.ChallengeAnswer.Count);

[ashishdhingra]

LGTM

[normj]

Version 2.1.1 of Amazon.Lambda.CognitoEvents has been released with this PR. Thanks for the fix!