Update Zulip send message action

[SeanTAllen]

Brief summary of what the changes does

[Please write a quick summary of the changes.]

Checklist

Please confirm with x:

• I own the copyright to the submitted changes and indemnify ponylang-mode from any copyright claim that might result from my not being the authorized copyright holder.
• I've read CONTRIBUTING.md
• I've used the latest version of package-lint to check for packaging issues, and addressed its feedback
• My elisp byte-compiles cleanly
• M-x checkdoc is happy with my docstrings
• I have confirmed some of these without doing them