specs: upgrade to Specl 11 custom matcher API.

* lib/zmacs/specs/spec_helper.lua (format_actual, match_minibuf)
(match_buffer, write_to_minibuf, write_to_buffer): Add missing
`self` parameter.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
travis: display the travis badge only for master builds.

* README.md (travis-ci status): Only master (Lua Zile) is setup
for travis builds, so don't show failures from other branches.

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