Using new complete --keep-order option for __fish_git_recent_commits

The primary motivation for --keep-order for `complete` was to support
something like commit history completions, which are returned by git in
reverse chronological order and make no sense alphabetically (they are
SHA1 hashes).

See #361 for more info.

share/completions/git.fish

@@ -427,7 +427,7 @@ complete -c git -n '__fish_git_needs_command' -a commit -d 'Record changes to th
 complete -c git -n '__fish_git_using_command commit' -l amend -d 'Amend the log message of the last commit'
 complete -f -c git -n '__fish_git_using_command commit' -a '(__fish_git_modified_files)'
 complete -f -c git -n '__fish_git_using_command commit' -l fixup -d 'Fixup commit to be used with rebase --autosquash'
-complete -f -c git -n '__fish_git_using_command commit; and __fish_contains_opt fixup' -a '(__fish_git_recent_commits)'
+complete -f -c git -n '__fish_git_using_command commit; and __fish_contains_opt fixup' -k -a '(__fish_git_recent_commits)'
 # TODO options
 
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