Bump shelljs to 0.8.4

v0.8.4 included a commit to prevent circular dependency warnings in Node 14. See: shelljs/shelljs@a1111ee

Author: skonves

package-lock.json

@@ -77,7 +77,7 @@
     "rimraf": "^2.6.3",
     "run-async": "^2.0.0",
     "semver": "^7.2.1",
-    "shelljs": "^0.8.3",
+    "shelljs": "^0.8.4",
     "text-table": "^0.2.0",
     "through2": "^3.0.1"
   },