Make webpack-cli optional peer

Author: eps1lon

package.json

@@ -117,6 +117,11 @@
     "webpack": "^4.0.0",
     "webpack-cli": "^3.0.0"
   },
+  "peerDependenciesMeta": {
+    "webpack-cli": {
+      "optional": true
+    }
+  },
   "author": "Tobias Koppers @sokra",
   "bugs": "https://github.com/webpack/webpack-dev-server/issues",
   "homepage": "https://github.com/webpack/webpack-dev-server#readme",