cookbook: ensure working version of setuptools_scm

stack/slapos.cfg

@@ -95,10 +95,16 @@ eggs =
   ${python-cachecontrol:egg}
   ${python-cliff:egg}
   ${python-cryptography:egg}
+  ${jsonschema:egg}
   pyOpenSSL
   slapos.cookbook
   slapos.libnetworkcache
 
+[jsonschema]
+recipe = zc.recipe.egg:custom
+egg = ${:_buildout_section_name_}
+setup-eggs = setuptools_scm
+
 [versions]
 setuptools = 40.4.3
 # Use SlapOS patched zc.buildout
@@ -214,6 +220,10 @@ attrs = 18.2.0
 # jsonschema==3.0.0a3
 pyrsistent = 0.14.5
 
+# Required by:
+# jsonschema==3.0.2
+setuptools-scm = 3.5.0
+
 # Required by:
 # cryptography==1.8.1
 ipaddress = 1.0.18