Make the changelog generation script work for release candidates too.

release

@@ -60,6 +60,7 @@ gbp dch \
    `if [ ${SNAPSHOT} = no -a -z ${SINCE} ]; then echo "--auto" ; fi` \
    --new-version="${NEW_VERSION}" \
    --ignore-branch \
+   --dch-opt=--force-bad-version \
    -- '*' ':!wiki' \
    || fatal "gbp dch failed."