Update to eslint-config-scratch@6.0.0 and associated fixes

package-lock.json

package.json

src/containers/blocks.jsx

src/containers/sound-editor.jsx

src/containers/stage.jsx

src/lib/audio/audio-util.js

src/lib/backpack-api.js

src/lib/libraries/.eslintrc.js

src/reducers/alerts.js

src/reducers/locales.js

test/smoke/browser.test.js

test/unit/reducers/alerts-reducer.test.js

test/unit/reducers/monitor-layout-reducer.test.js

test/unit/reducers/project-state-reducer.test.js

test/unit/util/audio-util.test.js