remove spurious a

Author: tbrowder

doc/Language/tables.pod6

@@ -28,7 +28,7 @@ other rows.
 
 2. Mixing visible and invisible column separators in the same table is
 illegal.
-a
+
 3. The only valid row separator characters are V<'_'>, V<'-'>, V<'+'>, V<' '>,
 V<'|'>, and V<'='>.