ash: Add missing Apache-2.0 to Cargo.toml license field

We already ship both license files in the published crate, have both
licenses listed in the `README`, and even `ash-window` already lists
both in `Cargo.toml`.

I found this while experimenting with shields.io badges, as there's a
special link that scrapes the license straight off of crates.io:
https://img.shields.io/crates/l/ash (and many more).  This might've been
nice to use except that it's outdated until we publish the next release,
and doesn't allow a nice link to either `LICENSE-XXX` file that we have
now.

README.md

@@ -6,7 +6,7 @@ A very lightweight wrapper around Vulkan
 [![Documentation](https://docs.rs/ash/badge.svg)](https://docs.rs/ash)
 [![Build Status](https://github.com/MaikKlein/ash/workflows/CI/badge.svg)](https://github.com/MaikKlein/ash/actions?workflow=CI)
 [![LICENSE](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE-MIT)
-[![LICENSE](https://img.shields.io/badge/license-apache-blue.svg)](LICENSE-APACHE)
+[![LICENSE](https://img.shields.io/badge/license-Apache--2.0-blue.svg)](LICENSE-APACHE)
 [![Join the chat at https://gitter.im/MaikKlein/ash](https://badges.gitter.im/MaikKlein/ash.svg)](https://gitter.im/MaikKlein/ash?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 ## Overview

ash/Cargo.toml

@@ -3,7 +3,7 @@ name = "ash"
 version = "0.37.0+1.3.219"
 authors = ["maik klein <maikklein@googlemail.com>"]
 description = "Vulkan bindings for Rust"
-license = "MIT"
+license = "MIT OR Apache-2.0"
 repository = "https://github.com/MaikKlein/ash"
 readme = "../README.md"
 keywords = ["vulkan", "graphic"]