Update htmx.md

[rtmorgan]

Corrected server-sent-events-examples repo reference.

[rtmorgan]

Thank you Mark for this blog as well as your books and conference presentations - I've learned so much from your clear and pleasant instruction!

[rtmorgan]

Mark, as I am looking at the incredible examples you have in both the 'server-sent-events-examples' and 'htmx-examples' repos I realize the blog's htmx sse example could just as easily point to the SSE example in 'htmx-examples' (as it is a better match to the sse source example in the blog) as to the examples in 'server-sent-events-examples'.

So the main request of the PR is a bump to correct the websocket-examples link at the end of the blog's htmx 'Server-Sent Events' section.

With that - I now have more htmx examples to work through!