Fixes un bug empêchant la détection

src/build-manifest.js

@@ -15,7 +15,7 @@ fs.readdir(workingDirectory, (err, files) => {
 	if (err) { throw err };	// If IO error, exit with an error message
 
 	// If there is already a theme.json silentely exit and let mocha running afterwards
-	if (!files.find(file => path.extname(file) == '.json')) exit(0);
+	if (files.find(file => path.extname(file) == '.json')) exit(0);
 
 	// construct a JSON object
 	let theme = new Object();