rst2man.py -> rst2man

[bwarden]

Fix build failure:

rst2man.py "docs/swupd.1.rst" > "docs/swupd.1.tmp" && mv -f "docs/swupd.1.tmp" "docs/swupd.1"
rst2man.py "docs/swupd-alias.7.rst" > "docs/swupd-alias.7.tmp" && mv -f "docs/swupd-alias.7.tmp" "docs/swupd-alias.7"
rst2man.py "docs/swupd-update.service.4.rst" > "docs/swupd-update.service.4.tmp" && mv -f "docs/swupd-update.service.4.tmp" "docs/swupd-update.service.4"
rst2man.py "docs/update-triggers.target.4.rst" > "docs/update-triggers.target.4.tmp" && mv -f "docs/update-triggers.target.4.tmp" "docs/update-triggers.target.4"
/bin/sh: line 1: rst2man.py: command not found
rst2man.py "docs/swupd-update.timer.4.rst" > "docs/swupd-update.timer.4.tmp" && mv -f "docs/swupd-update.timer.4.tmp" "docs/swupd-update.timer.4"
/bin/sh: line 1: rst2man.py: command not found
/bin/sh: line 1: rst2man.py: command not found
/bin/sh: line 1: rst2man.py: command not found

[bryteise]

Ah nice, thanks!