Documentation/git-multi-pack-index.txt: fix typo

Remove the extra space character between "tracked" and "by", which dates
back to when this paragraph was originally written in cff9711
(multi-pack-index: prepare for 'expire' subcommand, 2019-06-10).

Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

Documentation/git-multi-pack-index.txt

@@ -70,7 +70,7 @@ verify::
 	Verify the contents of the MIDX file.
 
 expire::
-	Delete the pack-files that are tracked 	by the MIDX file, but
+	Delete the pack-files that are tracked by the MIDX file, but
 	have no objects referenced by the MIDX. Rewrite the MIDX file
 	afterward to remove all references to these pack-files.