Use HTTPS in Gemfile

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Use 'off_t' for 'lseek' return value

'lseek' may return a negative value and 'off_t' is signed. This fixes
compilation warnings issued by Clang.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Merge branch 'fixes/lseek-return-value' of git://github.com/jvirtanen/pstore
Merge branch 'fixes/gemfile' of git://github.com/jvirtanen/pstore