Get release-date from first NEWS entry instead of modification time of configure.ac

configure.ac

@@ -13,8 +13,8 @@ AX_SET_VERSION_INFO
 
 # Automatically update release date based on configure.ac date
 AS_CASE([$host_os],
-    [linux*],[release_date=`date +"%Y-%m-%d" -r ${srcdir}/configure.ac`],
-    [*],[release_date=$(date -r "$(stat -f %m ${srcdir}/configure.ac)" +"%Y-%m-%d")])
+    [linux*],[release_date=$(sed -n 's/^Knot DNS .* (\(.*\))/\1/p;q;' ${srcdir}/NEWS)],
+    [*],[release_date=$(sed -n 's/^Knot DNS .* (\(.*\))/\1/p;q;' ${srcdir}/NEWS)])
 AC_SUBST([RELEASE_DATE], $release_date)
 
 # Set compiler compatibility flags