index.php: don't throw your arms in the air when the output is an array

index.php

@@ -109,7 +109,7 @@ putenv('LC_ALL=en_US.UTF-8');
 exec('bundle exec rake generate 2>&1', $output, $ret);
 $OUTPUT = implode("\n", $output);
 
-if ($ret != 0 or strpos($output, "error") !== FALSE) {
+if ($ret != 0 or strpos($OUTPUT, "error") !== FALSE) {
 	echo "build error (rake returned $ret), output:\n\n";
 	echo var_export($output, true);
 	die();