Consider updating license field

[andrewliebenow]

Consider changing ASL 2.0 here:

docker-ce-packaging/rpm/SPECS/docker-ce.spec

Line 10 in 22c4243

License: ASL 2.0

to Apache-2.0.

I'm not sure if Fedora is the source of truth in these matters, or if this would cause breakage downstream, but I think generally people are moving to SPDX.

https://docs.fedoraproject.org/en-US/legal/allowed-licenses/ lists Apache-2.0 as the SPDX identifier and ASL 2.0 as a "Legacy Abbreviation" for Apache License 2.0.