fix: use permissive version range for postcss peerDependency

Author: ZauberNerd

package.json

@@ -89,6 +89,6 @@
     "postcss-modules": "0.4.0"
   },
   "peerDependencies": {
-    "postcss": "5.0.18"
+    "postcss": "5"
   }
 }