lui-autopaste.el: fix bpaste helper

It seems the bpaste service recently changed it's API and defaulted to
running on the https port. In lieu of any official documentation I
traced the post request in my browser and saw what was getting sent.

Signed-off-by: Alex Bennée <alex@bennee.com>
Merge pull request #94 from stsquad/fix-bpaste

lui-autopaste.el: fix bpaste helper