subtree: use "^{commit}" instead of "^0"

LukeShu · gitster · commit bbffb023830f · 2021-04-28T16:47:18.000+09:00
They are synonyms.  Both are used in the file.  ^{commit} is clearer, so
"standardize" on that.

Signed-off-by: Luke Shumaker &lt;lukeshu@datawire.io&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
@@ -316,7 +316,7 @@ find_latest_squash () {
 			main="$b"
 			;;
 		git-subtree-split:)
-			sub="$(git rev-parse "$b^0")" ||
+			sub="$(git rev-parse "$b^{commit}")" ||
 			die "could not rev-parse split hash $b from commit $sq"
 			;;
 		END)
@@ -363,7 +363,7 @@ find_existing_splits () {
 			main="$b"
 			;;
 		git-subtree-split:)
-			sub="$(git rev-parse "$b^0")" ||
+			sub="$(git rev-parse "$b^{commit}")" ||
 			die "could not rev-parse split hash $b from commit $sq"
 			;;
 		END)
