incorrect var name

Missed as the old file wasn't wiped out, it just completed with a hidden warning

inc/composer/class-plugin.php

@@ -108,6 +108,6 @@ public function generate_module_manifest() {
 		}
 
 		// Write the loader file.
-		file_put_contents( $vendor_dir . DIRECTORY_SEPARATOR . 'modules.php', $package_list );
+		file_put_contents( $vendor_dir . DIRECTORY_SEPARATOR . 'modules.php', $module_loader );
 	}
 }