upgrade to webpack 4 (and remove some unused dependencies)

Author: Hamms

package.json

@@ -29,7 +29,7 @@
     "babel-core": "^6.26.0",
     "babel-eslint": "^8.0.3",
     "babel-jest": "^22.1.0",
-    "babel-loader": "^7.1.2",
+    "babel-loader": "^7.1.4",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-plugin-transform-class-properties": "^6.23.0",
     "babel-plugin-transform-es2015-classes": "^6.9.0",
@@ -38,12 +38,9 @@
     "codecov": "^3.0.0",
     "eslint": "^3.19.0",
     "eslint-plugin-babel": "^4.1.2",
-    "file-loader": "^1.1.6",
-    "html-webpack-plugin": "^2.30.1",
     "jest": "^22.1.3",
-    "prop-types": "^15.6.0",
-    "webpack": "^3.8.1",
-    "webpack-dev-server": "^2.9.5"
+    "webpack": "^4.8.1",
+    "webpack-cli": "^2.1.3"
   },
   "jest": {
     "coverageDirectory": "./coverage/",