unix: fix a comment typo in signal.c

PR-URL: https://github.com/libuv/libuv/pull/2318
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Vladimír Čunát <v@cunat.cz>

src/unix/signal.c

@@ -375,7 +375,7 @@ static int uv__signal_start(uv_signal_t* handle,
 
   /* Short circuit: if the signal watcher is already watching {signum} don't
    * go through the process of deregistering and registering the handler.
-   * Additionally, this avoids pending signals getting lost in the small time
+   * Additionally, this avoids pending signals getting lost in the small
    * time frame that handle->signum == 0.
    */
   if (signum == handle->signum) {