Typo fix (#6254)

files/en-us/web/javascript/inheritance_and_the_prototype_chain/index.html

@@ -113,7 +113,7 @@ <h2 id="Using_prototypes_in_JavaScript">Using prototypes in JavaScript</h2>
 console.log( doSomething.prototype );
 //  It does not matter how you declare the function; a
 //  function in JavaScript will always have a default
-//  prototype property — with one one exception: an arrow
+//  prototype property — with one exception: an arrow
 //  function doesn't have a default prototype property:
 const doSomethingFromArrowFunction = () =&gt; {};
 console.log( doSomethingFromArrowFunction.prototype );