Fix for undocumented dependency on service name "web"

[cmeans]

Hi,

I'm currently evaluating docker-dev for use within my company, and encountered the issue were we'd need to rename the container being exposed to "web".

I was later able to create a PR, but here's the suggested code change:

File: app.go
Replace:

			for _, container := range containers {
				for _, containerName := range container.Names {
					if containerName == expectedContainerName {
						id = container.ID
					}
				}
			}

With:

			if id == "" {
				for _, container := range containers {
					for _, containerPort := range container.Ports {
						if containerPort.PublicPort == uint16(app.Port) {
							id = container.ID
						}
					}
				}
			}

You would then be able to drop the expectedContainerName var also.

It seems to work in my limited testing, but perhaps there's additional issues I'm not aware of.

What do you think?