build(deps-dev): bump webextension-polyfill from 0.4.0 to 0.5.0

Bumps [webextension-polyfill](https://github.com/mozilla/webextension-polyfill) from 0.4.0 to 0.5.0.
- [Release notes](https://github.com/mozilla/webextension-polyfill/releases)
- [Commits](mozilla/webextension-polyfill@0.4.0...0.5.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

package-lock.json

@@ -47,7 +47,7 @@
     "vue-loader": "^15.7.1",
     "vue-template-compiler": "^2.6.10",
     "web-ext": "^3.1.1",
-    "webextension-polyfill": "^0.4.0",
+    "webextension-polyfill": "^0.5.0",
     "webpack": "^4.41.2",
     "webpack-cli": "^3.3.9",
     "webpack-merge": "^4.2.2"