git-merge.txt: modernize word choice in "True merge" section

The "True merge" section of the 'git merge' documentation mentions that
in case of conflicts, the conflicted working tree files contain "the
result of the "merge" program". This probably refers to RCS's 'merge'
program, which is mentioned further down under "How conflicts are
presented".

Since it is not clear at that point of the document which program is
referred to, and since most modern readers probably do not relate to RCS
anyway, let's just write "the merge operation" instead.

Signed-off-by: Philippe Blain <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: phil-blain

Documentation/git-merge.txt

@@ -194,7 +194,7 @@ happens:
    versions: stage 1 stores the version from the common ancestor,
    stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
    can inspect the stages with `git ls-files -u`).  The working
-   tree files contain the result of the "merge" program; i.e. 3-way
+   tree files contain the result of the merge operation; i.e. 3-way
    merge results with familiar conflict markers `<<<` `===` `>>>`.
 5. No other changes are made.  In particular, the local
    modifications you had before you started merge will stay the