chore(dependencies): Bump webpack from 3.8.1 to 3.9.1

Bumps [webpack](https://github.com/webpack/webpack) from 3.8.1 to 3.9.1.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/compare/v3.8.1...v3.9.1)

package.json

@@ -104,7 +104,7 @@
     "vue-style-loader": "^3.0.3",
     "vue-template-compiler": "^2.5.9",
     "vue-test-utils": "^1.0.0-beta.1",
-    "webpack": "^3.8.1",
+    "webpack": "^3.9.1",
     "webpack-bundle-analyzer": "^2.9.1",
     "webpack-dev-middleware": "^1.10.0",
     "webpack-hot-middleware": "^2.16.1",

yarn.lock

@@ -6536,9 +6536,9 @@ webpack-sources@^1.0.1:
     source-list-map "^2.0.0"
     source-map "~0.5.3"
 
-webpack@^3.8.1:
-  version "3.8.1"
-  resolved "https://registry.yarnpkg.com/webpack/-/webpack-3.8.1.tgz#b16968a81100abe61608b0153c9159ef8bb2bd83"
+webpack@^3.9.1:
+  version "3.9.1"
+  resolved "https://registry.yarnpkg.com/webpack/-/webpack-3.9.1.tgz#9a60aa544ed5d4d454c069e3f521aa007e02643c"
   dependencies:
     acorn "^5.0.0"
     acorn-dynamic-import "^2.0.0"