Updating "caveat" to "warning"

Updating "caveat" to "warning" as suggested in #155

content/docs/introducing-jsx.md

@@ -81,7 +81,7 @@ const element = <img src={user.avatarUrl}></img>;
 
 Don't put quotes around curly braces when embedding a JavaScript expression in an attribute. You should either use quotes (for string values) or curly braces (for expressions), but not both in the same attribute.
 
->**Caveat:**
+>**Warning:**
 >
 >Since JSX is closer to JavaScript than HTML, React DOM uses `camelCase` property naming convention instead of HTML attribute names.
 >