Update root selector for vr unit

Author: James Kolce

lib/compile.js

@@ -7,7 +7,9 @@ module.exports = (file) => {
   }).css;
 
   return postcss([
-    require('postcss-vertical-rhythm'),
+    require('postcss-vertical-rhythm')({
+      rootSelector: ':root'
+    }),
     require('postcss-custom-media'),
     require('postcss-media-minmax'),
     require('autoprefixer')

test/fixtures/verticalRhythm/verticalRhythm.css

@@ -1,4 +1,4 @@
-body {
+:root {
   font: 16px/2 serif;
 }
 

test/fixtures/verticalRhythm/verticalRhythm.scss

@@ -1,4 +1,4 @@
-body {
+:root {
   font: 16px/2 serif;
 }