Apply some small tweaks to Rivets.Binding::unbind.

@@ -49,11 +49,11 @@ class Rivets.Binding
     el = e.target or e.srcElement
     Rivets.config.adapter.publish @model, @keypath, getInputValue el
 
-  # Unsubscribes from the model and the element
+  # Unsubscribes from the model and the element.
   unbind: =>
     Rivets.config.adapter.unsubscribe @model, @keypath, @set
 
-    if @type in bidirectionals
+    if @bindType is "bidirectional"
       @el.removeEventListener 'change', @publish
 
 # A collection of bindings for a parent element.