Escape tracking class names

src/plugins/tracking.js

@@ -1,11 +1,11 @@
 import _ from 'lodash'
 
 export default function() {
-  return function({ addUtilities, config }) {
+  return function({ addUtilities, config, e }) {
     const utilities = _.fromPairs(
       _.map(config('tracking'), (value, modifier) => {
         return [
-          `.tracking-${modifier}`,
+          `.${e(`tracking-${modifier}`)}`,
           {
             'letter-spacing': value,
           },