dl: add go1.11beta3
dl: add go1.11beta3

Change-Id: If1e946924e81f19f7bcfc367581e1c11397c45f6
Reviewed-on: https://go-review.googlesource.com/127817
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/dl