fix: pin eslint-plugin-n to ^15.7 to support node 14

[MichaelGoberling]

Description

Version ^16.0 of eslint-plugin-n doesn't support Node 14, but aio still does. Pin to ^15.7 for now

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #230 (7ac9f43) into master (a70a8a3) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #230   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          313       313           
  Branches        44        44           
=========================================
  Hits           313       313           

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