dl: add go1.11beta2
dl: add go1.11beta2

Change-Id: I3a51fa60810d733564882e8887e0edc51df03cb6
Reviewed-on: https://go-review.googlesource.com/125136
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/dl