fix: fixtures/packaging/webpack/prod/package.json & fixtures/packaging/webpack/prod/yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-FORMDATA-10841150

Author: snyk-bot

fixtures/packaging/webpack/prod/package.json

@@ -2,7 +2,7 @@
   "private": true,
   "name": "webpack-prod-fixture",
   "dependencies": {
-    "webpack": "^1.14.0"
+    "webpack": "^2.2.0"
   },
   "scripts": {
     "build": "rm -f output.js && webpack --config config.js"