chore(package): update postcss-cli to version 7.0.0

Closes #12

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "del-cli": "^1.0.0",
     "live-server": "^1.2.0",
     "nsp": "^2.6.3",
-    "postcss-cli": "^4.0.0",
+    "postcss-cli": "^7.0.0",
     "postcss-cssnext": "^2.11.0",
     "postcss-import": "^10.0.0",
     "stylelint": "^8.0.0"