hooks:pre-commit: Update to git's current version

The template has changed since I've added it.

meta/git/hooks/pre-commit

@@ -13,22 +13,24 @@ if git rev-parse --verify HEAD >/dev/null 2>&1; then
 	against=HEAD
 else
 	# Initial commit: diff against an empty tree object
-	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+	against=$(git hash-object -t tree /dev/null)
 fi
 
+# If you want to allow non-ASCII filenames set this variable to true.
+allownonascii=$(git config --type=bool hooks.allownonascii)
+
 # Redirect output to stderr.
 exec 1>&2
 
 # Check that all filenames include only ASCII characters.
-allownonascii=$(git config --bool hooks.allownonascii)
 if [ "$allownonascii" != "true" ]; then
-	# We exploit the fact that the printable range starts at the space character
-	# and ends with tilde.
+	# We exploit the fact that the printable range starts at the space
+	# character and ends with tilde.
 	# Note that the use of brackets around a tr range is ok here, (it's
 	# even required, for portability to Solaris 10's /usr/bin/tr), since
 	# the square bracket bytes happen to fall in the designated range.
 	num_nonascii=$(
-		git diff --cached --name-only --diff-filter=AR -z $against \
+		git diff-index --cached --name-only --diff-filter=A -z $against \
 		| LC_ALL=C tr -d '[ -~]\0' \
 		| wc -c
 	)