ZP-1039 Don't use die() to terminate in error case for gab-sync.

Released under the Affero GNU General Public License (AGPL) version 3.

tools/gab-sync/gab-sync.php

@@ -70,7 +70,8 @@ include_once(SYNC_CONFIG);
         GabSyncCLI::RunCommand();
     }
     catch (Exception $ex) {
-        die(get_class($ex) . ": ". $ex->getMessage() . PHP_EOL);
+        fwrite(STDERR, get_class($ex) . ": ". $ex->getMessage() . PHP_EOL);
+        exit(1);
     }