fix(deps): update dependency args to v2

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
args	dependencies	major	^1.5.1 -> ^2.0.0

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Release Notes

dart-lang/args (args)

v2.4.2

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• Change the validation of mandatory options; they now perform validation when
  the value is retrieved (from the ArgResults object), instead of when the
  args are parsed.
• Require Dart 2.19.

v2.4.1

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• Add a CONTRIBUTING.md file; move the publishing automation docs from the
  readme into the contributing doc.
• Added package topics to the pubspec file.

v2.4.0

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• Command suggestions will now also suggest based on aliases of a command.
• Introduce getter Command.suggestionAliases for names that cannot be used as
  aliases, but will trigger suggestions.

v2.3.2

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• Require Dart 2.18

v2.3.1

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• Switch to using package:lints.
• Address an issue with the readme API documentation (#​211).
• Populate the pubspec repository field.

v2.3.0

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• Add the ability to group commands by category in usage text.

v2.2.0

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• Suggest similar commands if an unknown command is encountered, when using the
  CommandRunner.
  • The max edit distance for suggestions defaults to 2, but can be configured
    using the suggestionDistanceLimit parameter on the constructor. You can
    set it to 0 to disable the feature.

v2.1.1

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• Fix a bug with mandatory options which caused a null assertion failure when
  used within a command.

v2.1.0

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• Add a mandatory argument to require the presence of an option.
• Add aliases named argument to addFlag, addOption, and addMultiOption,
  as well as a public findByNameOrAlias method on ArgParser. This allows
  you to provide aliases for an argument name, which eases the transition from
  one argument name to another.

v2.0.0

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• Stable null safety release.

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