dl: add go1.15rc2
dl: add go1.15rc2

Change-Id: Id09672733dc989d620c3792c40b78659d5779f43
Reviewed-on: https://go-review.googlesource.com/c/dl/+/247403
Run-TryBot: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/dl