Update DMS "Translation Center" link: from 404 to Transifex

From 404 to the DMS Transifex translation project.

Ref. https://github.com/pagelines/DMS/tree/1.1/language/readme.txt

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	PageLines I18n
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	Join our translation task force at
	www.transifex.com/projects/p/pagelines-dms/

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