fix appearance of error message - .errors is outdated

fix error warning appearance on installation page. To improve the recognition value

cc @owncloud/designers 

Before:
![error-box-on-installation-before](https://f.cloud.github.com/assets/245432/1681604/d0609c30-5d97-11e3-9630-296ebfb65cab.png)
After:
![error-box-on-installation-after](https://f.cloud.github.com/assets/245432/1681605/d060eed8-5d97-11e3-95b3-647b7bc1b16e.png)