delta-islands: use Q_() for island count

The progress message "Marked %d islands, done." is marked for
translation with _(), which gives translators a single form for
every count. It reads wrongly when only one island is marked, and
languages with more than two plural forms cannot translate it
correctly.

Use Q_() with a singular and a plural form so the right one is
picked from island_counter.

Signed-off-by: Okhuomon Ajayi <okhuomonajayi54@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

delta-islands.c

@@ -496,7 +496,9 @@ void load_delta_islands(struct repository *r, int progress)
 	free_remote_islands(ild.remote_islands);
 
 	if (progress)
-		fprintf(stderr, _("Marked %d islands, done.\n"), island_counter);
+		fprintf(stderr, Q_("Marked %d island, done.\n",
+				   "Marked %d islands, done.\n", island_counter),
+			island_counter);
 }
 
 void propagate_island_marks(struct repository *r, struct commit *commit)