docs: fix Message link in messages examples README

[mcalthrop]

Fixed the link to the Message object in the messages examples README was incorrect.

Please note: to test this PR, I ran the following commands:

npm install

npm run dist

This resulted in an error:

So I ran this command:

ENABLE_FEATURE_V4=true npm run dist

And that command succeeded.

[mefellows]

Thanks, great spot - that needs to be updated. I'll get that sorted next week - thanks for the PR!