i18n: make "wiki" lowercase

Spotted by Siebrand
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Openid-error-openid-convert-not-allowed-forced-provider/en

Change-Id: I4a0684a071826e62798257e789f2c8f87d66af76
Merge "i18n: make "wiki" lowercase"