update vendor

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>

vendor/github.com/containerd/continuity/fs/du.go

@@ -0,0 +1,22 @@
+package fs
+
+import "context"
+
+// Usage of disk information
+type Usage struct {
+	Inodes int64
+	Size   int64
+}
+
+// DiskUsage counts the number of inodes and disk usage for the resources under
+// path.
+func DiskUsage(roots ...string) (Usage, error) {
+	return diskUsage(roots...)
+}
+
+// DiffUsage counts the numbers of inodes and disk usage in the
+// diff between the 2 directories. The first path is intended
+// as the base directory and the second as the changed directory.
+func DiffUsage(ctx context.Context, a, b string) (Usage, error) {
+	return diffUsage(ctx, a, b)
+}