Update listener port for express app

[p1johnson]

Resolves #30 which describes that following the How To guide Build and deploy to Azure Kubernetes Service with Azure Pipelines will result in the application being unavailable via the service.

[p1johnson]

@juliakm could you have a look at this PR please, which ties in with the Docs PR from yesterday?

[AlinDanielFerenczi]

The docker file needs to expose port 8080 as well in order for this to work.

[p1johnson]

I found that the example worked without including EXPOSE 8080 in the Dockerfile. My understanding is that the EXPOSE instruction is for documentation purposes. EXPOSE

[AlinDanielFerenczi]

I just made a test with this and it did not work until exposing the port. I think the instruction works as a firewall rule.

[p1johnson]

@AlinDanielFerenczi for the sake of completeness I've added the instruction EXPOSE 8080 to the Dockerfile.

[juliakm]

Thanks @p1johnson!