Bump shelljs from 0.7.8 to 0.8.5 in /frontend

Bumps [shelljs](https://github.com/shelljs/shelljs) from 0.7.8 to 0.8.5.
- [Release notes](https://github.com/shelljs/shelljs/releases)
- [Changelog](https://github.com/shelljs/shelljs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/shelljs/shelljs/compare/v0.7.8...v0.8.5)

---
updated-dependencies:
- dependency-name: shelljs
  dependency-type: direct:production
...
Signed-off-by: Ndependabot[bot] <support@github.com>

frontend/package.json

@@ -67,7 +67,7 @@
     "postcss-url": "^7.2.1",
     "rimraf": "^2.6.0",
     "sass-loader": "^7.1.0",
-    "shelljs": "^0.7.6",
+    "shelljs": "^0.8.5",
     "sinon": "^4.0.0",
     "sinon-chai": "^2.8.0",
     "uglifyjs-webpack-plugin": "^1.1.1",
@@ -148,7 +148,7 @@
     "rimraf": "^2.6.0",
     "sass-loader": "^7.1.0",
     "semver": "^5.3.0",
-    "shelljs": "^0.7.6",
+    "shelljs": "^0.8.5",
     "sinon": "^4.0.0",
     "sinon-chai": "^2.8.0",
     "uglifyjs-webpack-plugin": "^1.1.1",