Fix rendering of unquoted empty attributes.

Author: kevincox

lib/index.js

@@ -82,6 +82,8 @@ function render (tree, options) {
       if (typeof obj[key] === 'string') {
         if (quoteAllAttributes || obj[key].match(ATTRIBUTE_QUOTES_REQUIRED)) {
           attr += ' ' + key + '="' + obj[key].replace(/"/g, '"') + '"'
+        } else if (obj[key] === '') {
+          attr += ' ' + key
         } else {
           attr += ' ' + key + '=' + obj[key]
         }

test/render.test.js

@@ -327,6 +327,15 @@ describe('PostHTML Render', function () {
         expect(render(fixture, options)).to.eql(expected)
       })
 
+      it('Required Empty', function () {
+        var options = { quoteAllAttributes: false }
+
+        var fixture = { tag: 'script', attrs: { async: '' } }
+        var expected = '<script async></script>'
+
+        expect(render(fixture, options)).to.eql(expected)
+      })
+
       it('Closing slash', function () {
         var options = {
           closingSingleTag: 'slash',