Bump shelljs and jshint

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


Removes `shelljs`

Updates `jshint` from 2.10.1 to 2.13.6
- [Release notes](https://github.com/jshint/jshint/releases)
- [Changelog](https://github.com/jshint/jshint/blob/main/CHANGELOG.md)
- [Commits](jshint/jshint@2.10.1...2.13.6)

---
updated-dependencies:
- dependency-name: shelljs
  dependency-type: indirect
- dependency-name: jshint
  dependency-type: direct:development
...

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

package.json

@@ -25,7 +25,7 @@
   "devDependencies": {
     "debug": "2.6.9",
     "js-beautify": "1.8.9",
-    "jshint": "2.10.1",
+    "jshint": "2.13.6",
     "leche": "2.2.3",
     "mocha": "5.2.0",
     "nock": "13.3.3",