fix: remove undefined reference to `this.region`

[zlalvani]

In packages/serverless-offline-sqs/src/sqs.js, there is an undefined reference to this.region that causes the awsRegion parameter to not be passed to lambda invocations.

For context, I am using a parsing library that considers awsRegion to be a required field.

[GonzaloSaad]

Hello! Can we merge this! It would be good to have this live!