t9145-git-svn-master-branch.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/t9145-git-svn-master-branch.sh

@@ -17,8 +17,8 @@ test_expect_success 'git svn clone --stdlayout sets up trunk as master' '
 	git svn clone -s "$svnrepo" g &&
 	(
 		cd g &&
-		test x`git rev-parse --verify refs/remotes/origin/trunk^0` = \
-		     x`git rev-parse --verify refs/heads/master^0`
+		test x$(git rev-parse --verify refs/remotes/origin/trunk^0) = \
+		     x$(git rev-parse --verify refs/heads/master^0)
 	)
 '