autonumber in sequence diagram not working

[DuncanButler]

Describe the bug
renders graph correctly, but output console reports error in diagram

To Reproduce
from mermaid book, valid script shows issue:
`---
title: User Signup Flow

sequenceDiagram
autonumber
actor Browser
participant Sign Up Service
participant User Service
participant Kafka

Browser->>Sign Up Service: GET /sign_up
activate Sign Up Service
Sign Up Service-->>Browser: 200 OK (HTML Page)
deactivate Sign Up Service

Browser->>Sign Up Service: POST /sign_up
activate Sign Up Service
Sign Up Service->>Sign Up Service: Validate input

alt invalid input
    Sign Up Service-->>Browser: Error
else valid input
    Sign Up Service->>User Service: POST /users
    activate User Service
    User Service--)Kafka: User Created Event Published
    note left of Kafka: other services take action based on this event
    User Service-->>Sign Up Service: 201 Created (User)
    deactivate User Service
    Sign Up Service-->>Browser: 301 Redirect (Login page)
end
deactivate Sign Up Service

`
Expected behavior
shoud display numbers for each sequence line

Side note:
This is the only error I have found so far, its been a bonus being able to work with this extension installed, thanks for all the hard work developing this tooling to handle mmd files.

[DuncanButler]

autonumber does not work in the mermaid live editor either, but editing the config and adding,

"sequence": { "showSequenceNumbers": true }

does make the number appear correctly.

it would be nice to have either option in the editor