Change range for the Sewer portal vault to D:3-6 (was 3-7).

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7701 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dploog  on November 30, 2008
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