Bump stylelint from 15.6.0 to 16.13.2 #96

Job	Run time
Test CSS and JS (18.x)	7s
Build (jekyll gem) (3.9, ubuntu-latest, 2.7)	1m 3s
Build (github-pages gem)	42s
Build (jekyll gem) (3.9, ubuntu-latest, 3.1)	23s
Build (jekyll gem) (3.9, macos-latest, 2.7)	1m 19s
Build (jekyll gem) (3.9, macos-latest, 3.1)	24s
Build (jekyll gem) (3.9, windows-latest, 2.7)	2m 45s
Build (jekyll gem) (3.9, windows-latest, 3.1)	3m 3s
Build (jekyll gem) (4.3, ubuntu-latest, 2.7)	1m 28s
Build (jekyll gem) (4.3, ubuntu-latest, 3.1)	30s
Build (jekyll gem) (4.3, macos-latest, 2.7)	1m 49s
Build (jekyll gem) (4.3, macos-latest, 3.1)	32s
Build (jekyll gem) (4.3, windows-latest, 2.7)	4m 5s
Build (jekyll gem) (4.3, windows-latest, 3.1)	3m 41s
	21m 51s

Provide feedback