ensure working version of setuptools_scm

Install setuptools_scm before jsonschema (which has it in setup_requires) so that the version can be controlled by buildout

See merge request !768

stack/slapos.cfg

@@ -95,6 +95,7 @@ eggs =
   ${python-cachecontrol:egg}
   ${python-cliff:egg}
   ${python-cryptography:egg}
+  ${jsonschema:egg}
   pyOpenSSL
   slapos.cookbook
 
@@ -107,6 +108,11 @@ eggs =
   ${python-cryptography:egg}
   slapos.toolbox
 
+[jsonschema]
+recipe = zc.recipe.egg:custom
+egg = ${:_buildout_section_name_}
+setup-eggs = setuptools_scm
+
 # Install a slapos command with networkcache enabled in ${buildout:bin-directory}
 [slapos-command]
 recipe = zc.recipe.egg
@@ -230,6 +236,10 @@ 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