Update package.json

与webpack-cli保持匹配，后面统一升级

Author: songyumeng

package.json

@@ -102,7 +102,7 @@
     "uglify-es": "^3.3.9",
     "url-loader": "^1.0.1",
     "watchify": "^3.9.0",
-    "webpack": "^4.1.1",
+    "webpack": "4.1.1",
     "webpack-cli": "^2.0.12",
     "webpack-dev-middleware": "^3.2.0",
     "webpack-node-externals": "^1.6.0",