buildout: define versions constraints with [versions]

For consistency, defined all versions constraints in version section.
Also don't mention python34 since ZODB no longer supports python3.4

buildout.cfg

@@ -10,6 +10,11 @@ parts =
 # Avoid breakage in 4.4.5:
 zope.testrunner = >= 4.4.6
 
+[versions:python2]
+Sphinx = < 2
+pygments = < 2.6
+sphinxcontrib-websupport = < 1.2
+
 [test]
 recipe = zc.recipe.testrunner
 eggs =
@@ -49,19 +54,10 @@ eggs =
     ${coverage-test:eggs}
 interpreter = py
 
-[sphinx_egg]
-eggs = Sphinx
-
-[sphinx_egg:python2 or python34]
-eggs =
-    Sphinx < 2
-    pygments < 2.6
-    sphinxcontrib-websupport < 1.2
-
 [sphinx]
 recipe = zc.recipe.egg
 eggs =
-    ${sphinx_egg:eggs}
+    Sphinx
     docutils
     ZODB
     sphinxcontrib_zopeext