VOL-1255: Fixed an issue with the proxy implementation

- Had to change the model slightly to mimic a polymorphic behaviour

Change-Id: I12017cdfedf5c0ed05243245aa2a811556222e0f
diff --git a/db/model/revision.go b/db/model/revision.go
index a7b0c39..3912f67 100644
--- a/db/model/revision.go
+++ b/db/model/revision.go
@@ -29,7 +29,7 @@
 	GetBranch() *Branch
 	Get(int) interface{}
 	GetData() interface{}
-	GetNode() *Node
+	GetNode() *node
 	UpdateData(data interface{}, branch *Branch) Revision
 	UpdateChildren(name string, children []Revision, branch *Branch) Revision
 	UpdateAllChildren(children map[string][]Revision, branch *Branch) Revision