title: How to replace nth character of a string with another
body: <p>How could I replace <em>nth</em> character of a <code>String</code> with another one?</p>
  
  <pre><code>func replace(myString:String, index:Int, newCharac:Character) -&gt; String {
      // Write correct code here
      return modifiedString
  }
  </code></pre>
  
  <p>For example, <code>replace("House", 2, "r")</code> should be equal to <code>"Horse"</code>.</p>