enqueue_script doesn’t work with HTML5 blank theme

I’m not sure but it might have something to do with the html5blank_protocol_relative() function used by HTML5 Blank Theme.
You could try removing the filters at L# 382 & 383 of the functions.php file.

// Protocol relative URLs for enqueued scripts
add_filter( 'script_loader_src', 'html5blank_protocol_relative' );
// Protocol relative URLs for enqueued styles
add_filter( 'style_loader_src' , 'html5blank_protocol_relative' );

The problem shouldn’t be related to the wp_head() call, since the starter theme already has it in place.