[toml/en] fix code not rendering (#4221)

The json code block renders fine in Github Flavored Markdown on Github, but not on the learnxinyminutes.com/docs/toml page. Because there isn't any syntax highlighting for this section anyway, I switched it to vanilla code block.

toml.html.markdown

@@ -274,7 +274,8 @@ The equivalent in JSON would be:
 
 The equivalent in JSON would be:
 
-```json
+```
+
 {
   "fruit": [
     {