dl: add go1.12.8 and go1.11.13

Go 1.12.8 and Go 1.11.13 have been released¹, add commands for them.

¹ https://groups.google.com/d/msg/golang-announce/65QixT3tcmg/DrFiG6vvCwAJ

Change-Id: Ic70cc930f2a34aff096274a036470c37c930cd68
Reviewed-on: https://go-review.googlesource.com/c/dl/+/190178
Reviewed-by: Filippo Valsorda <filippo@golang.org>
diff --git a/go1.11.13/main.go b/go1.11.13/main.go
new file mode 100644
index 0000000..8f2ddad
--- /dev/null
+++ b/go1.11.13/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 go1.11.13 command runs the go command from Go 1.11.13.
+//
+// To install, run:
+//
+//     $ go get golang.org/dl/go1.11.13
+//     $ go1.11.13 download
+//
+// And then use the go1.11.13 command as if it were your normal go
+// command.
+//
+// See the release notes at https://golang.org/doc/devel/release.html#go1.11.minor
+//
+// File bugs at https://golang.org/issues/new
+package main
+
+import "golang.org/dl/internal/version"
+
+func main() {
+	version.Run("go1.11.13")
+}
diff --git a/go1.12.8/main.go b/go1.12.8/main.go
new file mode 100644
index 0000000..cbb9063
--- /dev/null
+++ b/go1.12.8/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 go1.12.8 command runs the go command from Go 1.12.8.
+//
+// To install, run:
+//
+//     $ go get golang.org/dl/go1.12.8
+//     $ go1.12.8 download
+//
+// And then use the go1.12.8 command as if it were your normal go
+// command.
+//
+// See the release notes at https://golang.org/doc/devel/release.html#go1.12.minor
+//
+// File bugs at https://golang.org/issues/new
+package main
+
+import "golang.org/dl/internal/version"
+
+func main() {
+	version.Run("go1.12.8")
+}