Feat: Added default fallback for CLI

[adampash]

Addresses #263

I considered automatically printing the help after the error message, but I decided it would get annoying to see the whole error message if you just entered a typo. It also made it more difficult to focus in on the fact that there was and error in the first place. So I went with this.

I pulled in chalk, since you're using it elsewhere, but if you don't like it, I can remove it!

Last: In an ideal world, we'd look at the text of the command and see if it's close to an existing lux command and present that to the user, like a "did you mean..." — but I'm trying to avoid letting this creep too far for a simple feature addition. 😄

[zacharygolba]

That's a good call and I totally agree with you. It's important that we gracefully handle this error and it's more or less bonus points if we implement fuzziness like the git cli down the road.

[zacharygolba]

These empty console.log's are a little hard to understand. I'm assuming this is to add a line break? If so, I suggest we do the following (It's not any more pretty but it's a bit more obvious what's going on imo):

const { EOL } = require('os');

function commandNotFound(cmd) {
  console.log(`${EOL}  ${red(cmd)} isn't a valid command${EOL}`);
  console.log(`  Type ${green('lux --help')} for a full list of commands${EOL}`);
}

os.EOL is used to determine the appropriate line breaks for the platform Lux is installed on.

[zacharygolba]

👏 This works great! I just made a few minor suggestions above.