stack/slapos: Version up Jinja to 2.11

Since Jinja 2.11 it's possible to do nice tests against true, false and
others, which is important for various type checks.

stack/slapos.cfg

@@ -142,7 +142,7 @@ zc.recipe.egg = 2.0.3+slapos003
 # Use own version of h.r.download to be able to open .xz and .lz archives
 hexagonit.recipe.download = 1.7.post4
 
-Jinja2 = 2.9.5
+Jinja2 = 2.11.2
 Importing = 1.10
 MarkupSafe = 1.0
 PyYAML = 3.13