chore(package): update postcss to version 7.0.30

Author: greenkeeper[bot]

package.json

@@ -90,7 +90,7 @@
     "jest-transform-css": "^2.0.0",
     "marked": "^1.0.0",
     "node-sass": "^4.14.0",
-    "postcss": "^7.0.27",
+    "postcss": "^7.0.30",
     "react-test-renderer": "^16.13.1",
     "rollup": "^2.7.3",
     "rollup-plugin-filesize": "^8.0.0",