Bump serialization version on WorkspaceView

Since we've replaced views with models, the 'PaneContainer' deserializer
now loads a model instead of a view, which isn't what we want at this
layer.

src/workspace-view.coffee

@@ -41,7 +41,7 @@ class WorkspaceView extends View
   Serializable.includeInto(this)
   atom.deserializers.add(this, PaneView, PaneRowView, PaneColumnView, EditorView)
 
-  @version: 2
+  @version: 3
 
   @configDefaults:
     ignoredNames: [".git", ".svn", ".DS_Store"]