fix: fix syntax error

fix #3

Author: yutahaga

index.js

@@ -1,7 +1,7 @@
 const pseudoElements = require('./pseudo-elements')
 
 module.exports = function({addVariant, e}) {
-  const escape = e || x => x
+  const escape = e || (x => x)
   pseudoElements.forEach(pseudo => {
     addVariant(pseudo, ({modifySelectors, separator}) => {
       modifySelectors(({className}) => {