Bump grunt-concurrent from 1.0.1 to 2.3.1 in /js

Bumps [grunt-concurrent](https://github.com/sindresorhus/grunt-concurrent) from 1.0.1 to 2.3.1.
- [Release notes](https://github.com/sindresorhus/grunt-concurrent/releases)
- [Commits](sindresorhus/grunt-concurrent@1.0.1...v2.3.1)

---
updated-dependencies:
- dependency-name: grunt-concurrent
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

js/package.json

@@ -21,7 +21,7 @@
     "grunt-cli": "~0.1.6",
     "grunt-contrib-jshint": "*",
     "jshint-stylish": "^2.1.0",
-    "grunt-concurrent": "~1.0.0",
+    "grunt-concurrent": "~2.3.1",
     "grunt-contrib-concat": "~0.1.2",
     "grunt-contrib-less": "~0.6.4",
     "grunt-contrib-watch": "~0.2.0",