Change "Language search" to "Search for a language"

Suggested at https://phabricator.wikimedia.org/T138235 .
This brings ULS closer to the mobile language search interface
in MediaWiki.

src/jquery.uls.core.js

@@ -36,7 +36,7 @@
 						<input type="text" class="uls-filterinput uls-languagefilter"\
 							id="uls-languagefilter" data-clear="uls-languagefilter-clear"\
 							data-suggestion="uls-filtersuggestion"\
-							placeholder="Language search" autocomplete="off">\
+							placeholder="Search for a language" autocomplete="off">\
 					</div>\
 				</div>\
 			</div>\