Update package.json

package.json

@@ -38,7 +38,7 @@
     "classnames": "2.2.6",
     "computed-style-to-inline-style": "3.0.0",
     "copy-webpack-plugin": "6.4.1",
-    "core-js": "^3.30.0",
+    "core-js": "2.5.7",
     "css-loader": "^1.0.1",
     "es6-object-assign": "1.1.0",
     "file-loader": "2.0.0",
@@ -144,7 +144,7 @@
     "web-audio-test-api": "0.5.2",
     "webpack": "4.46.0",
     "webpack-cli": "3.3.12",
-    "webpack-dev-server": "4.0.0",
+    "webpack-dev-server": "3.11.2",
     "webpack-sources": "3.2.3"
   },
   "jest": {