chore(deps-dev): bump stylus from 0.63.0 to 0.64.0

Bumps [stylus](https://github.com/stylus/stylus) from 0.63.0 to 0.64.0.
- [Release notes](https://github.com/stylus/stylus/releases)
- [Changelog](https://github.com/stylus/stylus/blob/dev/Changelog.md)
- [Commits](stylus/stylus@0.63.0...0.64.0)

---
updated-dependencies:
- dependency-name: stylus
  dependency-version: 0.64.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

package.json

@@ -161,7 +161,7 @@
     "stylelint-config-standard": "34.0.0",
     "stylelint-csstree-validator": "3.0.0",
     "stylelint-scss": "5.3.2",
-    "stylus": "^0.63.0",
+    "stylus": "^0.64.0",
     "stylus-loader": "^8.1.0",
     "vue-jest": "^3.0.7",
     "vue-loader": "15.11.1",