Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/golang.org/x/sys/unix/ioctl.go

@@ -0,0 +1,30 @@
+// Copyright 2018 The Go 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 darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package unix
+
+import "runtime"
+
+// IoctlSetWinsize performs an ioctl on fd with a *Winsize argument.
+//
+// To change fd's window size, the req argument should be TIOCSWINSZ.
+func IoctlSetWinsize(fd int, req uint, value *Winsize) error {
+	// TODO: if we get the chance, remove the req parameter and
+	// hardcode TIOCSWINSZ.
+	err := ioctlSetWinsize(fd, req, value)
+	runtime.KeepAlive(value)
+	return err
+}
+
+// IoctlSetTermios performs an ioctl on fd with a *Termios.
+//
+// The req value will usually be TCSETA or TIOCSETA.
+func IoctlSetTermios(fd int, req uint, value *Termios) error {
+	// TODO: if we get the chance, remove the req parameter.
+	err := ioctlSetTermios(fd, req, value)
+	runtime.KeepAlive(value)
+	return err
+}