Merge pull request rust-lang#4058 from tgross35/edition-2015

[0.2] Explicitly set the edition to 2015

Author: tgross35

Cargo.toml

@@ -4,6 +4,7 @@ version = "0.2.164"
 authors = ["The Rust Project Developers"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
+edition = "2015"
 repository = "https://github.com/rust-lang/libc"
 homepage = "https://github.com/rust-lang/libc"
 documentation = "https://docs.rs/libc/"