Enforce(meta-brainscales) pynn@0.9.4 or later

BrainScaleS' PyNN depends on PyNN.serialization… which is only available at 0.9.4 or later…

packages/meta-brainscales/package.py

@@ -54,7 +54,7 @@ class MetaBrainscales(Package):
     depends_on('py-pycodestyle')
     depends_on('py-pyelftools')
     depends_on('py-pylint')
-    depends_on('py-pynn')
+    depends_on('py-pynn@0.9.4:')
     depends_on('py-pyyaml')
     depends_on('py-scipy')
     depends_on('py-sqlalchemy')