Use gnome-text-editor to replace gedit in the introduction of the document

[linghengqian]

• Fixes https://github.com/MicrosoftDocs/WSL/issues/1681.
• Use gnome-text-editor to replace gedit in the introduction of the document.

[learn-build-service-prod[bot]]

Learn Build status updates of commit b1e4774:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
WSL/tutorials/gui-apps.md	:white_check_mark:Succeeded	View

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[mattwojo]

Awesome. Thanks for contributing this update @linghengqian!! Really appreciate your help staying up to date.