Fix strict issue

Strict Standards<:  Declaration of LuceneResult::getTitleSnippet()
should be compatible with that of SearchResult::getTitleSnippet()
in /usr/local/apache/common-local/php-1.24wmf15/extensions/MWSearch/MWSearch_body.php
on line 153

Change-Id: I2b724dd6abfd512b3212eb40c309ca8bd33cf11f