Fix broken install command

[lydell]

Regression from #465.

Before:

❯ ../bin/elm-test install truqu/elm-md5
I am having trouble with this argument:

    t

It is supposed to be a <package> value, like one of these:

    elm/html
    elm/http
    elm/svg
    elm/time

After:

❯ ../bin/elm-test install truqu/elm-md5
Here is my plan:

  Add:
    truqu/elm-md5            1.1.0
    zwilias/elm-utf-tools    2.0.1

Would you like me to update your elm.json accordingly? [Y/n]:
Success!

This happened because I thought the first argument of the .action callback is always an array. Wrong! The signature depends on the .command syntax provided:

program
  .command('name <one> <two> [three] [rest...]')
  .action((one: string, two: string, three: string | undefined, rest: Array<string>, cmd: Command) => {
    // Do stuff
  });

For the install command we have:

program
  .command('install <package>')
  .action((packageName: string, cmd: Command) => {})

Before we tried to destructure the first argument (thinking it was an array), so we only got the first letter of the package name.

Unfortunately our test suite doesn’t catch this.

[harrysarson]

Nice catch! Could you add a regression test?

[lydell]

Do you have any ideas on how to write one?

[lydell]

I figured it out.

[harrysarson]

It looks like travis has pulled macos support. I guess we cannot complain too much because we were getting it for free.

@lydell could you remove mac from travis just so we can get a green tick. Longer time we probably want to migrate to github actions.

Cc: @rtfeldman
Refs: https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing