Fix grammar error

tests/pass-dep/libc/libc-epoll.rs

@@ -103,7 +103,7 @@ fn test_epoll_socketpair() {
     assert!(check_epoll_wait::<8>(epfd, &[(expected_event, expected_value)]));
 }
 
-// This test first register a file description with a flag that does not lead to notification,
+// This test first registers a file description with a flag that does not lead to notification,
 // then EPOLL_CTL_MOD to add another flag that will lead to notification.
 fn test_epoll_ctl_mod() {
     // Create an epoll instance.