DOC: Fix map table's format

so the HTML doc parser can parse the table correctly
diff --git a/doc/configuration.txt b/doc/configuration.txt
index f6121ee..18da5b9 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -12415,9 +12415,9 @@
   -----------+--------------+-----------------+-----------------+---------------
     str      | end          | map_end         | map_end_int     | map_end_ip
   -----------+--------------+-----------------+-----------------+---------------
-             |              | map_reg         |                 |
-    str      | reg          +-----------------+ map_reg_int     | map_reg_ip
-             |              | map_regm        |                 |
+    str      | reg          | map_reg         | map_reg_int     | map_reg_ip
+  -----------+--------------+-----------------+-----------------+---------------
+    str      | reg          | map_regm        | map_reg_int     | map_reg_ip
   -----------+--------------+-----------------+-----------------+---------------
     int      | int          | map_int         | map_int_int     | map_int_ip
   -----------+--------------+-----------------+-----------------+---------------