Joomla 3 version has wrong XML manifest

https://github.com/pe7er/mod_db8404errors/blob/master/joomla3/mod_db8404errors.xml
needs to be changed from
```xml
<extension type="module" version="3.9" client="site" method="upgrade">
```
to
```xml
<extension type="module" version="3.9" client="administrator" method="upgrade">
```
