Some GitHub links in doc/index.html are now stale

[jschleus]

Some links in the "Examples" section of the file doc/index.html are now stale and must be updated probably by

http://lvc.github.com/pkgdiff/ -> https://lvc.github.io/pkgdiff/

[linuxhw]

Fixed. Thank you!