maint: fix a typo in rockspec.conf

* rockspec.conf (homepage): Use the correct project url!

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
travis: ensure availability of help2man.

* src/src.mk (docs/mkrockspecs.1): No need to call `missing` when
configure already sets HELP2MAN appropriately.
* travis.yml.in (install): Install help2man.
* .travis.yml: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>