Support in-place upgrades of new minio binary and releases. (#4961)

This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.

Updates are done safely by validating the downloaded
sha256 of the binary.

Fixes #4781

vendor/github.com/inconshreveable/go-update/hide_noop.go

@@ -0,0 +1,7 @@
+// +build !windows
+
+package update
+
+func hideFile(path string) error {
+	return nil
+}