fix: pin webpack version, fixes #3335

Author: haoqunjiang

packages/@vue/cli-service/package.json

@@ -66,7 +66,7 @@
     "thread-loader": "^1.2.0",
     "url-loader": "^1.1.2",
     "vue-loader": "^15.4.2",
-    "webpack": "4",
+    "webpack": ">=4 < 4.29",
     "webpack-bundle-analyzer": "^3.0.3",
     "webpack-chain": "^4.11.0",
     "webpack-dev-server": "^3.1.14",