Bump shelljs and update

Removes [shelljs](https://github.com/shelljs/shelljs). It's no longer used after updating ancestor dependency [update](https://github.com/update/update). These dependencies need to be updated together.


Removes `shelljs`

Updates `update` from 0.4.2 to 0.7.4
- [Release notes](https://github.com/update/update/releases)
- [Changelog](https://github.com/update/update/blob/master/CHANGELOG.md)
- [Commits](https://github.com/update/update/commits/0.7.4)

---
updated-dependencies:
- dependency-name: shelljs
  dependency-type: indirect
- dependency-name: update
  dependency-type: direct:production
...

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

package.json

@@ -23,7 +23,7 @@
     "sass": "^1.55.0",
     "semver": "^7.3.7",
     "set-value": "^4.1.0",
-    "update": "^0.4.2"
+    "update": "^0.7.4"
   },
   "devDependencies": {
     "gh-pages": "^3.2.3"