Babel should not silently remove unknown options after commander arguments

[JLHwung]

Q	A
Fixed Issues?	Fixes #4825
Patch: Bug Fix?	Yes
Tests Added + Pass?	Yes
Any Dependency Changes?	commander.js is bumped to v4.0.1
License	MIT

In this PR we bump commander.js to v4.0.1, which can throw on unknown options after arguments when an action handler is provided. To do so we register an empty action handler so that unknown options error can be thrown.

Impact analysis of upgrading commander.js from 2.8 to 4.0

Breaking changes from 2.0 to 3.0

• Change TypeScript to use overloaded function for .command.
  Not related
• custom event listeners: --no-foo on cli now emits option:no-foo (previously option:foo)
  Not related since we are not using custom event listeners
• default value: defining --no-foo after defining --foo leaves the default value unchanged (previously set it to false)
  Not related since we don't have any option that has both --no- and -- prefixes.

Breaking changes from 3.0 to 4.0

• keep command object out of program.args when action handler called
  Not related since we are not using the command object in an action handler
• Commander is only officially supported on Node 8 and above, and requires Node 6
  It should be fine since we will drop Node 6 and 8 soon, too. If CI is good we may say it should work on Node 6 from now on.
• Testing for no arguments is changed
  Not related since I can't find any .args.length usage in our codebase.

[nicolo-ribaudo]

Commander is only officially supported on Node 8 and above, and requires Node 6
It should be fine since we will drop Node 6 and 8 soon, too. If CI is good we may say it should work on Node 6 from now on.

Ok since CI is passing, but we should be ready to pin an exact version in the future if it stops working.