Bump uglify-js from 3.17.4 to 3.19.3

Bumps [uglify-js](https://github.com/mishoo/UglifyJS) from 3.17.4 to 3.19.3.
- [Release notes](https://github.com/mishoo/UglifyJS/releases)
- [Commits](mishoo/UglifyJS@v3.17.4...v3.19.3)

---
updated-dependencies:
- dependency-name: uglify-js
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

package.json

@@ -33,7 +33,7 @@
   "devDependencies": {
     "jshint": "^2.10.2",
     "ncp": "latest",
-    "uglify-js": "^3.4.10",
+    "uglify-js": "^3.19.3",
     "watch": "^1.0.2"
   }
 }