Update tokio-util to 0.7

[conblem]

Hello everybody

warp is curently using tokio-util 0.6 in february tokio-util 0.7 was released.
The changelog can be found here here.

In my opinion this should cause no breakage in warp and would reduce duplicate dependencies in my project.
warp uses hyper which in turn uses h2, h2 already updated to tokio-util 0.7 in this commit.
It would probably make sense to also create a pull request for hyper (which I could do).

I just ran cargo test to make sure everything works, as I could not find further instructions for testing.

Help and input would be appreciated!

Kind regards

[jxs]

thanks!