Update vendor (#1297)

vendor/golang.org/x/sys/unix/fcntl_darwin.go

@@ -16,3 +16,9 @@ func FcntlFlock(fd uintptr, cmd int, lk *Flock_t) error {
 	_, err := fcntl(int(fd), cmd, int(uintptr(unsafe.Pointer(lk))))
 	return err
 }
+
+// FcntlFstore performs a fcntl syscall for the F_PREALLOCATE command.
+func FcntlFstore(fd uintptr, cmd int, fstore *Fstore_t) error {
+	_, err := fcntl(int(fd), cmd, int(uintptr(unsafe.Pointer(fstore))))
+	return err
+}