chore: drop shelljs requirement

Author: Sam Harrison

package.json

@@ -17,7 +17,6 @@
     "inquirer": "^7.1.0",
     "qs": "^6.9.3",
     "semver": "^7.3.0",
-    "shelljs": "^0.8.3",
     "tsv": "^0.2.0",
     "twilio": "^3.43.0"
   },