refactor: remove gulp from the build

Plain npm scripts should be sufficient for our use case.

package.json

@@ -28,38 +28,35 @@
     "to-array": "0.1.4"
   },
   "devDependencies": {
-    "babel-core": "^6.24.1",
-    "babel-eslint": "4.1.7",
-    "babel-loader": "7.0.0",
+    "@babel/core": "^7.11.6",
+    "@babel/plugin-transform-object-assign": "^7.10.4",
+    "@babel/preset-env": "^7.11.5",
+    "babel-eslint": "^10.1.0",
+    "babel-loader": "^8.1.0",
     "babel-preset-es2015": "6.24.1",
     "base64-arraybuffer": "^0.1.5",
-    "concat-stream": "^1.6.0",
-    "derequire": "^2.0.6",
+    "eslint": "^6.8.0",
     "eslint-config-standard": "4.4.0",
     "eslint-plugin-standard": "1.3.1",
     "expect.js": "0.3.1",
-    "gulp": "^3.9.1",
-    "gulp-eslint": "1.1.1",
-    "gulp-file": "^0.3.0",
-    "gulp-istanbul": "^1.1.1",
-    "gulp-mocha": "^4.3.1",
-    "gulp-task-listing": "1.0.1",
     "has-cors": "^1.1.0",
-    "imports-loader": "^0.7.1",
     "istanbul": "^0.4.5",
     "mocha": "^3.3.0",
     "socket.io": "2.3.0",
     "socket.io-browsers": "^1.0.0",
-    "strip-loader": "0.1.2",
     "text-blob-builder": "0.0.1",
-    "webpack-merge": "4.1.2",
-    "webpack-stream": "3.2.0",
+    "webpack": "^4.44.2",
+    "webpack-cli": "^3.3.12",
+    "webpack-remove-debug": "^0.1.0",
     "zuul": "~3.11.1",
     "zuul-builder-webpack": "^1.2.0",
     "zuul-ngrok": "4.0.0"
   },
   "scripts": {
-    "test": "gulp test"
+    "test": "if test \"$BROWSERS\" = \"1\" ; then npm run test:browser; else npm run test:node; fi",
+    "test:node": "mocha --reporter dot --require test/support/server.js test/index.js",
+    "test:browser": "zuul test/index.js",
+    "build": "webpack --config ./support/webpack.config.js --config ./support/prod.config.js"
   },
   "contributors": [
     {