t/t6032-merge-large-rename.sh: use the $( ... ) construct for command substitution

The Git CodingGuidelines prefer the $(...) construct for command
substitution instead of using the backquotes `...`.

The backquoted form is the traditional method for command
substitution, and is supported by POSIX.  However, all but the
simplest uses become complicated quickly.  In particular, embedded
command substitutions and/or the use of double quotes require
careful escaping with the backslash character.

The patch was generated by:

for _f in $(find . -name "*.sh")
do
	perl -i -pe 'BEGIN{undef $/;} s/`(.+?)`/\$(\1)/smg'  "${_f}"
done

and then carefully proof-read.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6032-merge-large-rename.sh

@@ -20,7 +20,7 @@ test_expect_success 'setup (initial)' '
 
 make_text() {
 	echo $1: $2
-	for i in `count 20`; do
+	for i in $(count 20); do
 		echo $1: $i
 	done
 	echo $1: $3