Allow no output

On files that have no issues, `ruby -wc` gives no output.

Author: Arcanemagus

lib/main.js

@@ -40,6 +40,7 @@ export default {
         const execOpts = {
           stdin: fileText,
           stream: 'stderr',
+          allowEmptyStderr: true,
         };
         const output = await helpers.exec(this.executablePath, execArgs, execOpts);
         if (textEditor.getText() !== fileText) {