Save entries in Tree cache using indenting.

Change-Id: I6c62ac1fa45a8e8c348f5734541dc6b6269ab869

cache/treecache.go

diff --git a/cache/treecache.go b/cache/treecache.go
index 286ce07..a712d32 100644
--- a/cache/treecache.go
+++ b/cache/treecache.go
@@ -79,7 +79,7 @@
 		return err
 	}
 
-	content, err := json.Marshal(tree)
+	content, err := json.MarshalIndent(tree, "", " ")
 	if err != nil {
 		return err
 	}