javascript-101/running-code: lowercase attribute in example

Closes jquerygh-617

Author: xfq

page/javascript-101/running-code.md

@@ -31,7 +31,7 @@ The last option is to use the event handler attributes of HTML elements. This me
 ```
 <!-- Inline code directly on HTML elements being clicked. -->
 <a href="javascript:alert( 'Hello World' );">Click Me!</a>
-<button onClick="alert( 'Good Bye World' );">Click Me Too!</button>
+<button onclick="alert( 'Good Bye World' );">Click Me Too!</button>
 ```
 
 ### Placement