follow SPDX for short license text (#305)

rust-lang/cargo#2174 (comment)

Author: altendky

zstd-safe/Cargo.toml

@@ -7,7 +7,7 @@ description = "Safe low-level bindings for the zstd compression library."
 keywords = ["zstd", "zstandard", "compression"]
 categories = ["api-bindings", "compression"]
 repository = "https://github.com/gyscos/zstd-rs"
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 readme = "Readme.md"
 edition = "2018"
 rust-version = "1.64"