build: disable documention on xapian for travis-ci. --disable-documentation passed to configure doesn't work and I have a crash in sphinx that prevents testing. Use -enable-documentation=no which appears to be how 1.4.14 expects it at least. no-github-ci to disable testing for github as this change affects travis only at this point. If it works, I'll disable doc build on github to to save cycles.

Babel
Jinja2
MarkupSafe
Pygments
alabaster
certifi
charset-normalizer
docutils
idna
imagesize
packaging
pyparsing
requests
six
snowballstemmer
sphinxcontrib-applehelp
sphinxcontrib-devhelp
sphinxcontrib-htmlhelp
sphinxcontrib-jsmath
sphinxcontrib-qthelp
sphinxcontrib-serializinghtml
sphinxcontrib-websupport
urllib3