fix(package): update postcss to version 7.0.31

Closes #61

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "jscodeshift": "0.7.0",
     "loader-utils": "1.2.3",
     "parse5": "5.1.1",
-    "postcss": "7.0.24",
+    "postcss": "7.0.31",
     "postcss-load-config": "2.1.0"
   },
   "devDependencies": {