Is your feature request related to a problem? Please describe.

According to current specification for HTML 5 compliant browsers, the type attribute of script tags isn't required if the type is JavaScript. Modern browsers automatically identify omitted script types as JavaScript. No matter what value is sent as type attribute, type will be added, even sending an empty string.

JFactory::getDocument()->addScript('script.js', array(), array('type' => ''));
Becomes:
<script src="script.js" type=""></script>

Describe the solution you'd like

To avoid setting off any deprecated behavior (but also not break backwards compatibility), why not have it set so that if a user provides an empty string for type, the type attribute isn't set.

JFactory::getDocument()->addScript('script.js', array(), array('type' => ''));
Becomes:
<script src="script.js"></script>