chore(package): update postcss-import to version 9.1.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -49,7 +49,7 @@
     "es6-promise": "4.0.5",
     "nib": "1.1.2",
     "postcss": "5.2.7",
-    "postcss-import": "7.1.3",
+    "postcss-import": "9.1.0",
     "postcss-url": "5.1.2",
     "stylus": "0.54.5",
     "vow": "0.4.15"