PollOpt is deprecated for event trigger types in MIO

[vertexclique]

Looks like with mio 0.7.* PollOpt is not there anymore.
So we need to refactor the code to don't pass PollOpt along with interests.

[jdafont]

I’d like to take a swing at this!

[jdafont]

So, I've looked into the issue and I'm just going to summarize the findings here to save time for others.

Mio removed PollOpts from the public API here: tokio-rs/mio#975

The purpose of this was to reduce the scope of the API and no longer support oneshot events as described here: tokio-rs/mio#928

Mio simply drops the parameter since there is only the one supported mode now (Edge triggered). Fortunately, async-std only uses this in one spot:

async-std/src/net/driver/mod.rs

Lines 98 to 99 in 57974ae

	let opts = mio::PollOpt::edge();
	self.poller.register(source, token, interest, opts)?;

The solution here is to simply remove opts. But, this would only compile with Mio at version 0.7 of course. Is there a branch to convert async-std to mio 0.7?

[vertexclique]

@guiri14 Not in my knowledge. @stjepang Are you willing to?