Fixed missing export of card-markdown card and broken tests

no issue
- fixes rendering bug introduced in 0833b28557
- updates test generators/fixtures to use new card names

core/server/lib/mobiledoc/cards/card-markdown.js

@@ -4,4 +4,4 @@
 // our markdown-only editor was using the `card-markdown` card name
 const markdownCard = require('./markdown');
 
-module.exports = Object.assign(markdownCard, {name: 'card-markdown'});
+module.exports = Object.assign({}, markdownCard, {name: 'card-markdown'});

core/test/unit/lib/mobiledoc/converters/mobiledoc-converter_spec.js

@@ -6,16 +6,16 @@ describe('Convert mobiledoc to HTML ', function () {
         version: '0.3.1',
         atoms: [],
         cards: [
-            ['card-markdown',
+            ['markdown',
                 {
                     pos: 'top',
-                    card_name: 'card-markdown',
+                    card_name: 'markdown',
                     markdown: '#heading\n\n- list one\n- list two\n- list three'
                 }
             ],
-            ['card-html', {
+            ['html', {
                 pos: 'top',
-                card_name: 'card-html',
+                card_name: 'html',
                 html: '<p>HTML CARD</p>'
             }]
         ],

core/test/utils/fixtures/data-generator.js

@@ -11,8 +11,8 @@ DataGenerator.markdownToMobiledoc = function markdownToMobiledoc(content) {
         markups: [],
         atoms: [],
         cards: [
-            ['card-markdown', {
-                cardName: 'card-markdown',
+            ['markdown', {
+                cardName: 'markdown',
                 markdown: content || ''
             }]
         ],