Updated network option

[ajstanley]

This relates to issue 379.
External is not a recognized Docker network option, but it only fails on some machines. This ought to work anywhere, but its only been tested on a Mac, and an old one at that,

[misilot]

That's weird since external is defined in the documentation: https://docs.docker.com/compose/compose-file/06-networks/#external

[misilot]

Though it looks like the default is internal: false so would it be worth removing that config option all together?

[aOelschlager]

I would agree with @misilot that internal:false can be removed from the yaml files. In the tech call it was mentioned that the original purpose for this (external:true) was to be able to run isle 7 at the same time as isle-dc. I don't know if anyone is using it this way anymore but I highly doubt it.

[joecorall]

Before this PR I was getting

$ make starter
...
...
docker compose up -d --remove-orphans
Error response from daemon: network gateway not found
make: *** [starter] Error 1

$ echo $?
2

After this PR make starter gets past the docker compose up -d --remove-orphans command successfully.