refactor: drop else/if stmt

Since type is validated to be either 'js' or 'css' there was no point in
leaving a 3rd case (not js or css) open.

lib/main.js

@@ -229,7 +229,7 @@ module.exports = class Client {
 
         if (type === 'css') {
             return new CssWriter(files);
-        } else if (type === 'js') {
+        } else {
             const writer = new JsWriter(files, options);
 
             this.transforms.forEach(entry => {