Security: Upgrade @rails/webpacker and jest (#540)

* Security: Upgrade @rails/webpacker and jest

* Upgrade jest from 24.9.0 to 25.1.0
* Upgrade @rails/webpacker from 4.0.7 to 4.2.2

* Update test to use 1 worker

package.json

@@ -5,9 +5,9 @@
   "scripts": {
     "eslint": "eslint app/javascript --fix",
     "pretest": "rimraf .jest-cache",
-    "test": "jest --no-cache",
+    "test": "jest  -w 1 --no-cache",
-    "test:watch": "jest --watch --no-cache",
+    "test:watch": "jest -w 1 --watch --no-cache",
-    "test:coverage": "jest --no-cache --collectCoverage",
+    "test:coverage": "jest -w 1 --no-cache --collectCoverage",
     "webpacker-start": "webpack-dev-server -d --config webpack.dev.config.js --content-base public/ --progress --colors",
     "start:dev": "foreman start -f ./Procfile.dev"
   },
@@ -15,7 +15,7 @@
     "@babel/polyfill": "^7.6.0",
     "@babel/preset-env": "~7.3.4",
     "@rails/actioncable": "^6.0.0",
-    "@rails/webpacker": "^4.0.7",
+    "@rails/webpacker": "^4.2.2",
     "axios": "^0.19.0",
     "babel-helper-vue-jsx-merge-props": "^2.0.3",
     "babel-plugin-syntax-jsx": "^6.18.0",
@@ -59,7 +59,7 @@
     "@vue/test-utils": "^1.0.0-beta.29",
     "babel-core": "^7.0.0-bridge.0",
     "babel-eslint": "^10.0.1",
-    "babel-jest": "^24.9.0",
+    "babel-jest": "^25.1.0",
     "eslint": "^5.13.0",
     "eslint-config-airbnb": "^17.1.0",
     "eslint-config-prettier": "^4.0.0",
@@ -72,7 +72,7 @@
     "eslint-plugin-vue": "^5.2.3",
     "expect-more-jest": "^2.4.2",
     "husky": ">=1",
-    "jest": "^24.8.0",
+    "jest": "^25.1.0",
     "jest-serializer-vue": "^2.0.2",
     "jest-transform-stub": "^2.0.0",
     "lint-staged": ">=8",