Fix tense of error message

Thanks for putting this project together; really enjoying hacking with
it so far!

atom/browser/default_app/main.js

@@ -53,7 +53,7 @@ if (option.file && !option.webdriver) {
       dialog.showErrorBox('Error opening app', 'The app provided is not a valid atom-shell app, please read the docs on how to write one:\nhttps://github.com/atom/atom-shell/tree/master/docs');
       process.exit(1);
     } else {
-      console.error('App throwed an error when running', e);
+      console.error('App threw an error when running', e);
       throw e;
     }
   }