Update dependencies

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

@@ -0,0 +1,9 @@
+// Copyright 2019 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 aix darwin dragonfly freebsd nacl netbsd openbsd solaris
+
+package rand
+
+var defaultContextReader = &urandomReader{}