Replace "X-query" by "XQuery"

Spotted by Siebrand and Shirayuki
* http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Xquerygenerator/en_(2)
* http://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Xquerygenerator/en

Change-Id: If365b8c215235f63979af67c30f4648f5b4b3d27