Fix gravatar alt attribute for Addy (close #353)

index.html

@@ -255,7 +255,7 @@
 		</div>
 		<hr>
 		<footer class="credit">
-			<p>Brought to you by<a href="https://github.com/addyosmani"><img src="http://gravatar.com/avatar/96270e4c3e5e9806cf7245475c00b275?s=80" width="40" height="40" alt="Sindre Sorhus">Addy Osmani</a> and <a href="https://github.com/sindresorhus"><img src="http://gravatar.com/avatar/d36a92237c75c5337c17b60d90686bf9.png?s=80" width="40" height="40" alt="Sindre Sorhus">Sindre Sorhus</a></p>
+			<p>Brought to you by<a href="https://github.com/addyosmani"><img src="http://gravatar.com/avatar/96270e4c3e5e9806cf7245475c00b275?s=80" width="40" height="40" alt="Addy Osmani">Addy Osmani</a> and <a href="https://github.com/sindresorhus"><img src="http://gravatar.com/avatar/d36a92237c75c5337c17b60d90686bf9.png?s=80" width="40" height="40" alt="Sindre Sorhus">Sindre Sorhus</a></p>
 		</footer>
 	</div>
 	<script src="assets/jquery.min.js"></script>