Mark directories and blob nodes as non-deletable.

This should fix disappearing entries in the tree.

Change-Id: I0288fc31ec6a6b6117d5ed296f2bd86e88eb35d3
diff --git a/fs/gitilesfs.go b/fs/gitilesfs.go
index afc4261..7936604 100644
--- a/fs/gitilesfs.go
+++ b/fs/gitilesfs.go
@@ -105,6 +105,10 @@
 	mtime   time.Time
 }
 
+func (n *gitilesNode) Deletable() bool {
+	return false
+}
+
 func (n *gitilesNode) Utimens(file nodefs.File, atime *time.Time, mtime *time.Time, context *fuse.Context) (code fuse.Status) {
 	if mtime != nil {
 		n.mtimeMu.Lock()
@@ -332,6 +336,10 @@
 	return fuse.OK
 }
 
+func (n *dirNode) Deletable() bool {
+	return false
+}
+
 func newDirNode() nodefs.Node {
 	return &dirNode{nodefs.NewDefaultNode()}
 }