Update postcss-syntax in group default to the latest version 🚀 (#298)

## The dependency [postcss-syntax](https://github.com/gucong3000/postcss-syntax) was updated from `0.34.0` to `0.36.0`.
This version is **not covered** by your **current version range**.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

---

[Find out more about this release](https://github.com/gucong3000/postcss-syntax).

<details>
  <summary>FAQ and help</summary>

  There is a collection of [frequently asked questions](https://greenkeeper.io/faq.html). If those don’t help, you can always [ask the humans behind Greenkeeper](https://github.com/greenkeeperio/greenkeeper/issues/new).
</details>

---


Your [Greenkeeper](https://greenkeeper.io) bot 🌴

packages/configs/package.json

@@ -52,7 +52,7 @@
     "postcss-preset-env": "^6.4.0",
     "postcss-property-lookup": "^2.0.0",
     "postcss-reporter": "^6.0.0",
-    "postcss-syntax": "^0.34.0",
+    "postcss-syntax": "^0.36.0",
     "quickenv": "^0.0.6",
     "stylelint-config-standard": "^18.2.0"
   },