stack/slapos: version ↑ setuptools 40.4.3

jsonschema = 3.0.0a3 needs a recent setuptools, probably because it uses
setuptools_scm

stack/slapos.cfg

@@ -98,7 +98,7 @@ eggs =
   slapos.libnetworkcache
 
 [versions]
-setuptools = 33.1.1
+setuptools = 40.4.3
 # Use SlapOS patched zc.buildout
 zc.buildout = 2.5.2+slapos012
 # Use SlapOS patched zc.recipe.egg (zc.recipe.egg 2.x is for Buildout 2)