Fix highlighting in readme.md

wooorm · wooorm · commit d0664197e471 · 2017-02-05T19:19:56.000+01:00
diff --git a/README.md b/README.md
@@ -27,7 +27,7 @@ console.log(doc);
 
 Yields:
 
-```txt
+```markdown
 ## Hello **world!**
 ```
 
