Use drop instead of the toilet closure |_| ()

src/libstd/sys/unix/process/process_unix.rs

@@ -425,7 +425,7 @@ impl Process {
                 "invalid argument: can't kill an exited process",
             ))
         } else {
-            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ())
+            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
     }