Flat 4.1.0 is deprecated causing an npm warn

[JaredCE]

Prerequisites

• Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
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Description

when installing mocha 8.1.1, npm warns that flat 4.1.0 is deprecated.

Steps to Reproduce

run npm i -g mocha

Expected behavior: [What you expect to happen]

No warns

Actual behavior: [What actually happens]

npm WARN deprecated flat@4.1.0: Fixed a prototype pollution security issue in 4.1.0, please upgrade to ^4.1.1 or ^5.0.1.

Reproduces how often: [What percentage of the time does it reproduce?]

all the time

Versions

mocha 8.1.1
node 12
ubuntu bionic

[outsideris]

I check there is a deprecation warning in Ubuntu. It is from yarg-unparser, but the latest version of yarg-unparser(1.6.3) still have flat@4.1.0.

[hubiierik]

Issue opened in yargs-unparser: yargs/yargs-unparser#67