BUILD: scripts: fix typo in announce-release error message

It used to say the tag already existed instead of the opposite.
diff --git a/scripts/announce-release b/scripts/announce-release
index d70c33c..c4045ae 100755
--- a/scripts/announce-release
+++ b/scripts/announce-release
@@ -79,7 +79,7 @@
 fi
 
 if ! git show-ref --tags "v$NEW" >/dev/null; then
-	die "git tag v$NEW already exist, did you create the release ?"
+	die "git tag v$NEW doesn't exist, did you create the release ?"
 fi
 
 if [ -z "$OLD" ]; then