component/macros/virtual-env: Fix-up

`depends = {slapos-cookbook:recipe}` bug when `virtual-env-base` is used in an instance.cfg.

component/macros/virtual-env.cfg

@@ -28,11 +28,12 @@ init =
   """ % locals())
 
   if is_true(options.get('default-instance')):
+    cookbook = "{slapos-cookbook:recipe}"
     self.buildout.parse("""
     [.%(name)s.instance]
     recipe = slapos.recipe.template
     output = ${buildout:directory}/instance.cfg
-    depends = ${slapos-cookbook:recipe}
+    depends = $%(cookbook)s
     inline =
       [buildout]
       parts = publish