Ignore case when checking $_SERVER['HTTPS'] to load external js

@see #1176100: http/https font loading for the original issue.

The following sub-modules can fail to load external libraries over SSL due to a typo in their preprocess function:

• edge_fonts
• fonts_com
• google_fonts_api
• typekit_api

To fix, replace:

$_SERVER['HTTPS'] == 'on'

with:

0 == strcasecmp($_SERVER['HTTPS'], 'on')