build: Set "root": true, in .eslintrc.json
build: Set "root": true, in .eslintrc.json

This ensures that each repository's "npm test" command is fully
independent of wherever it might be in the filesystem.

Bug: T206485
Change-Id: If61d45abd8abea0adaf968a6819bad1905b0d812

wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage