fixed typo (#18)

04-components.html

@@ -49,7 +49,7 @@ <h2 key="data">{data}</h2>
 
 // Since React 16.2.0, we can use special "wrapper" components called fragments
 // that behave the same (no extra wrapper element created)
-// but remove the need to explitly set keys (fragments do this under the hood) and commas
+// but remove the need to explicitly set keys (fragments do this under the hood) and commas
 function MyComponent() {
  var data = "world"
  return (