Update sample app go.mod and go.sum to fix workflow

Issue #, if available: ECR publish workflow is failing with error:

go: updates to go.mod needed;

Description of changes:

cd sample-apps/http-server/
go get
go mod tidy

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

aws / aws-xray-sdk-go