patchbomb: use email.encoders instead of email.Encoders
No idea when this became a thing, but it exists for me in both 2.7 and 3.6.
Differential Revision: https://phab.mercurial-scm.org/D4222
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state