Lex Sample Bug: lex.go does not define LexResponse

[scconroy]

The sample here: https://github.com/aws/aws-lambda-go/blob/master/events/README_Lex.md

References:

*lex.LexResponse

However, this struct is not defined in lex.go:

https://github.com/aws/aws-lambda-go/blob/master/events/lex.go

Creating a custom struct worked as a workaround:

type LexResponse struct {
SessionAttributes map[string]string json:"sessionAttributes,omitempty"
DialogAction *events.LexDialogAction json:"dialogAction,omitempty"
}