t9901-git-web--browse.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/t9901-git-web--browse.sh

@@ -43,7 +43,7 @@ test_expect_success \
 	echo fake: "$@"
 	EOF
 	chmod +x "fake browser" &&
-	git config browser.w3m.path "`pwd`/fake browser" &&
+	git config browser.w3m.path "$(pwd)/fake browser" &&
 	test_web_browse w3m http://example.com/foo
 '