Bump stylelint from 15.7.0 to 15.10.0 #1677

Job	Run time
Test Ruby	1m 6s
Lint JavaScript / Run Standardx	31s
Lint Ruby / Run RuboCop	12s
Lint SCSS / Run Stylelint	30s
Security Analysis / Run Brakeman	9s
Test JavaScript / Run Jasmine	55s
	3m 23s

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