Update postcss-import to version 12.0.0 (postcss#235)

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "eslint": "^5.0.0",
     "eslint-config-problems": "1.1.0",
     "nyc": "^11.0.2",
-    "postcss-import": "^11.0.0",
+    "postcss-import": "^12.0.0",
     "prettier": "~1.14.0",
     "sugarss": "^1.0.0",
     "uuid": "^3.0.1"