Update dependencies

vendor/github.com/u-root/uio/rand/random_std.go

@@ -0,0 +1,31 @@
+// Copyright 2020 the u-root Authors. All rights reserved
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build plan9 windows
+
+package rand
+
+import (
+	"context"
+	"crypto/rand"
+)
+
+var defaultContextReader = &cryptoRandReader{}
+
+type cryptoRandReader struct{}
+
+// ReadContext implements a cancelable read.
+func (r *cryptoRandReader) ReadContext(ctx context.Context, b []byte) (n int, err error) {
+	ch := make(chan struct{})
+	go func() {
+		n, err = rand.Reader.Read(b)
+		close(ch)
+	}()
+	select {
+	case <-ctx.Done():
+		return 0, ctx.Err()
+	case <-ch:
+		return n, err
+	}
+}