dl: add go1.12

Change-Id: I6e38ef03e0da3ef64f17c816acc947152668f728
Reviewed-on: https://go-review.googlesource.com/c/163781
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: andybons

go1.12/main.go

@@ -0,0 +1,24 @@
+// Copyright 2019 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.
+
+// The go1.12 command runs the go command from Go 1.12.
+//
+// To install, run:
+//
+//     $ go get golang.org/dl/go1.12
+//     $ go1.12 download
+//
+// And then use the go1.12 command as if it were your normal go
+// command.
+//
+// See the release notes at https://golang.org/doc/go1.12
+//
+// File bugs at https://golang.org/issues/new
+package main
+
+import "golang.org/dl/internal/version"
+
+func main() {
+	version.Run("go1.12")
+}