Bump uglify-js from 3.14.1 to 3.17.4

Bumps [uglify-js](https://github.com/mishoo/UglifyJS) from 3.14.1 to 3.17.4.
- [Release notes](https://github.com/mishoo/UglifyJS/releases)
- [Commits](mishoo/UglifyJS@v3.14.1...v3.17.4)

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

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -41,7 +41,7 @@
     "sass-loader": "6.0.7",
     "showdown": "^2.1.0",
     "style-loader": "0.23.1",
-    "uglify-js": "3.14.1",
+    "uglify-js": "3.17.4",
     "uikit": "3.0.0-rc.26",
     "underscore": "1.13.6",
     "vue": "2.5.21",