Bump 100-expect length limit

[daurnimator]

https://daniel.haxx.se/blog/2020/02/27/expect-tweaks-in-curl/

Starting in curl 7.69.0 (due to ship on March 4, 2020) we catch up a little with the world around us and now libcurl will only automatically set the Expect: header if the amount of data to send in the body is larger than 1 megabyte. Yes, we raise the limit by 1024 times.

https://github.com/daurnimator/lua-http/blob/169c1a7586d39be1bf0d98b69934e8e8b08a87cd/http/request.lua#L342

[sudojarvis]

I would like work this issue. Could you please give some head start.

[daurnimator]

I think it is likely just changing the constant in the line I linked + writing a test case