made 'meadures' required for sensor

src/devices/sensor.jsonnet

@@ -1,5 +1,5 @@
-local types = import 'types.libsonnet';
 local entity = import 'entity.libsonnet';
+local types = import 'types.libsonnet';
 
 entity
 {
@@ -17,4 +17,6 @@ entity
       uniqueItems: true,
     },
   },
+
+  required+: ['measures'],
 }