Memoize normalize

src/module/normalize.js

@@ -1,9 +1,12 @@
 const CSSO = require('csso');
+const memoize = require('lodash/memoize');
+
+const fn = memoize((cssStr) =>
+  CSSO.minify(cssStr, { restructure: true })
+);
 
 module.exports = function Normalize(cssObj) {
-  return Promise.resolve(CSSO.minify(
-    cssObj.toString()
-  ), {
-    restructure: true
-  });
+  return Promise.resolve(
+    fn(cssObj.toString())
+  );
 };