Bump shelljs from 0.7.8 to 0.8.4

Bumps [shelljs](https://github.com/shelljs/shelljs) from 0.7.8 to 0.8.4.
- [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...v0.8.4)

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

package.json

@@ -85,7 +85,7 @@
     "request": "^2.88.0",
     "request-promise": "^4.2.2",
     "rimraf": "^2.5.2",
-    "shelljs": "^0.7.7",
+    "shelljs": "^0.8.4",
     "sinon": "^5.0.7",
     "ts-node": "^7.0.1",
     "tslint": "^5.11.0",