The below solution details moving the scripts to the bottom of your page template.
If you don't want to move your script files to the footer see this post on other ways to avoiding render-blocking.
Move <?php $scripts ?> to the bottom of your html.tpl.php file, just before <?php print $page_bottom; ?> and the closing </body> tag.
<?php print $scripts; ?> <?php print $page_bottom; ?> </body> </html>
Move <?php $scripts ?> to the bottom of your page.tpl.php file, just before <?php print $closure ?> and the closing </body> tag.
<?php print $scripts; ?> <?php print $closure; ?> </body> </html>
To quote the LABjs project page:
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