Bump vue-loader from 13.7.3 to 15.4.2

Bumps [vue-loader](https://github.com/vuejs/vue-loader) from 13.7.3 to 15.4.2.
- [Release notes](https://github.com/vuejs/vue-loader/releases)
- [Changelog](https://github.com/vuejs/vue-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vue-loader/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -122,7 +122,7 @@
     "stylus-loader": "^3.0.1",
     "url-loader": "^0.5.9",
     "vue-html-loader": "^1.2.4",
-    "vue-loader": "^13.0.5",
+    "vue-loader": "^15.4.2",
     "vue-style-loader": "^3.0.1",
     "vue-template-compiler": "^2.6.10",
     "webpack": "^3.5.2",