Jmsserializerbundle: Example code for "Changing the Object Constructor" section does not show on the web page.

[rgembalik]

http://jmsyst.com/bundles/JMSSerializerBundle/master/configuration#changing-the-object-constructor
Mentioned section should contain configuration examples mentioned in the source code here:
https://github.com/schmittjoh/JMSSerializerBundle/blob/master/Resources/doc/configuration.rst#changing-the-object-constructor

At the time of writing this section is followed up by the next section which confuses the reader.

[goetas]

PR are welcome :)

[kinow]

@goetas confirmed in the website that it's now looking OK! So I reckon this issue can also be closed :tada:

Thanks for reviewing the pull request so quickly!

[goetas]

thank to you for taking the time for this improvement