Update dependency commander to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
commander	dependencies	major	^5.1.0 -> ^6.0.0

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Release Notes

tj/commander.js

v6.0.0

Compare Source

Added

• add support for variadic options ([#​1250])
• allow options to be added with just a short flag ([#​1256])
• throw an error if there might be a clash between option name and a Command property, with advice on how to resolve ([#​1275])

Fixed

• Options which contain -no- in the middle of the option flag should not be treated as negatable. ([#​1301])

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