Changed protocal to HTTPS for sourced loads.

https://geoext.github.io/geoext2/
gh_pages use HTTPS, so anything being loaded insecurely may cause "Blocked loading mixed active content" which is not easy to get around in Firefox and Chrome. Internet Explorer offers a button to "Show all content" after saying "Only secure content is being displayed."

I verified that the two changed URLs work correctly of HTTPS. 

This does not seem to change much on the main page, but makes a big difference for the examples. Except that cdn.sencha.com does not seem to support HTTPS.