Update postcss dependencies

postcss.config.js

@@ -0,0 +1,19 @@
+const postcssEasyImport = require('postcss-easy-import');
+const postcssNested = require('postcss-nested');
+const postcssCustomMedia = require('postcss-custom-media');
+const postcssCssVariables = require('postcss-css-variables');
+const postcssMqPacker = require('css-mqpacker');
+const postcssAutoprefixer = require('autoprefixer');
+
+module.exports = {
+  plugins: [
+    postcssEasyImport(),
+    postcssNested(),
+    postcssCustomMedia(),
+    postcssCssVariables(),
+    postcssMqPacker(),
+    postcssAutoprefixer({
+      browsers: '> 5%',
+    }),
+  ],
+};