fix SSE unwrap

[yoshuawuyts]

Reported in https://twitter.com/fasterthanlime/status/1271398187484491776. Thanks!

[yoshuawuyts]

Fixing CI in #589. Once that passes we should re-run CI here.

[yoshuawuyts]

Okay, quite convinced this is an issue with crates.io, GitHub Actions, or the interaction between them. I can't reproduce this locally with either Windows or Linux; so just going to pray this passes.

Merging this!

[fasterthanlime]

@yoshuawuyts note that there's another insert_header in upgrade

edit: that's the one you fixed - there's another one in endpoint, here:

tide/src/sse/endpoint.rs

Line 61 in 1858cc0

res.res.insert_header("Cache-Control", "no-cache").unwrap();