Bump grunt-shell from 3.0.1 to 4.0.0 (closes #179)

Bumps [grunt-shell](https://github.com/sindresorhus/grunt-shell) from 3.0.1 to 4.0.0.
- [Release notes](https://github.com/sindresorhus/grunt-shell/releases)
- [Commits](https://github.com/sindresorhus/grunt-shell/compare/v3.0.1...v4.0.0)

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

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

Change-Id: I0752c07471aed93b76670ecd7436007246a541af
diff --git a/package.json b/package.json
index c372e9a..bfe28de 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,7 @@
     "grunt-contrib-requirejs": "^1.0.0",
     "grunt-contrib-watch": "^1.1.0",
     "grunt-sass": "^3.1.0",
-    "grunt-shell": "^3.0.1",
+    "grunt-shell": "^4.0.0",
     "grunt-terser": "^1.0.0",
     "imagemin": "^8.0.1",
     "optipng-bin": "^6.0.0",