Fixed some bugs in Zend\Config\Reader code examples

[This comment](http://framework.zend.com/manual/2.3/en/modules/zend.config.reader.html#comment-1482863835) mentions a bug in the `Zend\Config\Reader\XML` code sample:

> I think on the example for XML, it should be
echo $data['database']['params']['dbname']['value']; // prints "dbproduction"
not
echo $data['database']['params']['dbname']; // prints "dbproduction"
Also the XML has an excess encoding="utf-8"?>?> --> excess

Fixed those bugs and added some missing semicolons in the code samples.