Merge pull request #5475 from learningequality/dependabot/npm_and_yarn/stylus-0.64.0

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

Author: akolson

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",