Merge pull request #346 from navytux/y/cifix

buildout: Fix CI

/reviewed-on https://github.com/zopefoundation/ZODB/pull/346
/reviewed-by @d-maurer

buildout.cfg

@@ -9,6 +9,8 @@ parts =
 [versions]
 # Avoid breakage in 4.4.5:
 zope.testrunner = >= 4.4.6
+# sphinx_rtd_theme depends on docutils<0.17
+docutils = < 0.17
 
 [versions:python2]
 Sphinx = < 2

doc/requirements.txt

 Sphinx
 # Silence dependabot claiming a security issue in older versions:
-pygments >= 2.7.4
+pygments >= 2.7.4 ; python_version >= '3'
+# pygments 2.6 stopped supporting py2
+pygments <  2.6   ; python_version <  '3'
 docutils
 ZODB
 sphinxcontrib_zopeext