Add singlejar to the java tools zip.

Closes #7951.

PiperOrigin-RevId: 242421452
diff --git a/src/merge_zip_files.sh b/src/merge_zip_files.sh
index 9907bca..c148a9a 100755
--- a/src/merge_zip_files.sh
+++ b/src/merge_zip_files.sh
@@ -56,7 +56,7 @@
 if [[ "$directory_prefix" == "-" ]]; then
   for curr_zip in "$@"
   do
-    unzip -q "$curr_zip" -d "$tmp_dir"
+    unzip -q -o "$curr_zip" -d "$tmp_dir"
   done
 
   cd "$tmp_dir"
@@ -65,7 +65,7 @@
   mkdir -p "$tmp_dir/$directory_prefix"
   for curr_zip in "$@"
   do
-    unzip -q "$curr_zip" -d "$tmp_dir/$directory_prefix"
+    unzip -q -o "$curr_zip" -d "$tmp_dir/$directory_prefix"
   done
 
   cd "$tmp_dir"