manual: Fix description of a table range example

* doc/org-manual.org (Range references): Correct statement about the
number of fields that an example range includes.

Reported-by: Sebastian Miele <sebastian.miele@gmail.com>
<87eeu8kzyj.fsf@gmail.com>

doc/org-manual.org

@@ -1901,7 +1901,7 @@ correctly.  Examples:
 | =$1..$3=      | first three fields in the current row                          |
 | =$P..$Q=      | range, using column names (see [[*Advanced features]])             |
 | =$<<<..$>>=   | start in third column, continue to the last but one            |
-| =@2$1..@4$3=  | six fields between these two fields (same as =A2..C4=)         |
+| =@2$1..@4$3=  | nine fields between these two fields (same as =A2..C4=)        |
 | =@-1$-2..@-1= | 3 fields in the row above, starting from 2 columns on the left |
 | =@I..II=      | between first and second hline, short for =@I..@II=            |