Reduce MSRV to 1.60 with minor change in RawFd type

Author: hoxxep

Cargo.toml

@@ -10,7 +10,7 @@ description = """
 An implementation of the GNU make jobserver for Rust
 """
 edition = "2021"
-rust-version = "1.66"
+rust-version = "1.60"
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2.50"

src/error.rs

@@ -1,5 +1,5 @@
 #[cfg(unix)]
-type RawFd = std::os::fd::RawFd;
+type RawFd = std::os::unix::io::RawFd;
 #[cfg(not(unix))]
 type RawFd = std::convert::Infallible;