Fix Nokogiri parser processing xml entity encoded characters

In Nori 2.4.0 there is a bug in a parser when it processes xml entity encoded characters
that is a common case for non-chars-parse-fixEnglish SOAP applications.

For example, if we have the next node:
```
<ns0:ASSIGNEDGROUP>&#x414;&#x435;&#x436;&#x443;&#x440;&#x43D;&#x430;&#x44F; &#x441;&#x43C;&#x435;&#x43D;&#x430; &#x41B;&#x41F;1.5</ns0:ASSIGNEDGROUP>
```
and we want to convert it to hash using Nori with Nokogiri parser, it is expected to be:
```ruby
{"ns0:ASSIGNEDGROUP"=>"Дежурная смена ЛП1.5"}
```
but current version of Nori converts it to:
```ruby
{"ns0:ASSIGNEDGROUP"=>"ДежурнаясменаЛП1.5"}
```
since every whitespace in source xml lies between two other nodes and looks like a non-significant crap.

The present patch fixes this case, still not touching behaviour in any other way.