add 'use strict'; to index.js

Author: ponelat

dist/swagger-ui.js

@@ -1,7 +1,9 @@
+'use strict';
+
 var pack = require('./package');
 var path = require('path');
 
 module.exports = {
     version: pack.version,
     dist: path.resolve(__dirname, 'dist')
-};
+};