build: Bump linting devDependencies to latest

 eslint-config-wikimedia      0.5.0  →   0.8.1
 + eslint-plugin-qunit                   3.3.0
 grunt-eslint                20.1.0  →  21.0.0
 grunt-stylelint              0.9.0  →  0.10.1
 stylelint                    8.2.0  →   9.2.0
 stylelint-config-wikimedia   0.4.2  →   0.4.3

Change-Id: I34518a652fe144df5215b82e7e0c3e74f9b46a0d
3 files changed