How to Modify Drupal 7 Bootstrap Theme Title?
This thing is come under $head_title variable on html.tpl.php.
So for changing this you need to override template_preprocess_html
where replace statement
$variables['head_title'] = implode(' | ', $head_title);
with
$variables['head_title'] = implode(' - ', $head_title);
I am assuming you have enough idea about overriding of templates.