Update /server example to be strong mode compliant

[Sfshaza]

The /server example, used here has not been updated to be strong mode compliant. This also affects the text in that codelab.

PRs welcome.

[Stargator]

@Sfshaza I can do that!

[Sfshaza]

Wow, @Stargator, thanks! I'm going to let @kwalrath review this one.

[Stargator]

So far it looks good. Had to restrict the dependency versions for two packages to prevent an error when running pub get or pub upgrade

Will continue to look at it this week

[Sfshaza]

Thanks!

[Stargator]

Sorry for the delay. I haven't forgotten. I'll have some time to continue this soon.