Reenable `allowUnknownFlags: false` when meow#197 is fixed

[msabramo]

In cli.js:

	// TODO: Disabled until https://github.com/sindresorhus/meow/issues/197 is fixed.
	// allowUnknownFlags: false,

Without this, users get strange, nonsensical errors when they provide an unknown flag:

$ node cli.js --foobar "I got your input right here"
Input required

[msabramo]

One way to fix this sooner rather than later is what I suggested in #33 (comment), but I think @sindresorhus might not want to go that way.