Upgrade postcss@6

perrin4869 · perrin4869 · commit 18395071d91c · 2017-07-19T13:39:27.000+09:00
diff --git a/package.json b/package.json
@@ -26,7 +26,7 @@
   },
   "homepage": "https://github.com/seaneking/postcss-position",
   "dependencies": {
-    "postcss": "^5.0.0"
+    "postcss": "^6.0.7"
   },
   "devDependencies": {
     "gulp-eslint": "^0.12.0",
