Update to tokio 1.1 (#2172)

## Issue Addressed

resolves #2129
resolves #2099 
addresses some of #1712
unblocks #2076
unblocks #2153 

## Proposed Changes

- Updates all the dependencies mentioned in #2129, except for web3. They haven't merged their tokio 1.0 update because they are waiting on some dependencies of their own. Since we only use web3 in tests, I think updating it in a separate issue is fine. If they are able to merge soon though, I can update in this PR. 

- Updates `tokio_util` to 0.6.2 and `bytes` to 1.0.1.

- We haven't made a discv5 release since merging tokio 1.0 updates so I'm using a commit rather than release atm. **Edit:** I think we should merge an update of `tokio_util` to 0.6.2 into discv5 before this release because it has panic fixes in `DelayQueue`  --> PR in discv5:  https://github.com/sigp/discv5/pull/58

## Additional Info

tokio 1.0 changes that required some changes in lighthouse:

- `interval.next().await.is_some()` -> `interval.tick().await`
- `sleep` future is now `!Unpin` -> https://github.com/tokio-rs/tokio/issues/3028
- `try_recv` has been temporarily removed from `mpsc` -> https://github.com/tokio-rs/tokio/issues/3350
- stream features have moved to `tokio-stream` and `broadcast::Receiver::into_stream()` has been temporarily removed -> `https://github.com/tokio-rs/tokio/issues/2870
- I've copied over the `BroadcastStream` wrapper from this PR, but can update to use `tokio-stream` once it's merged https://github.com/tokio-rs/tokio/pull/3384

Co-authored-by: realbigsean <seananderson33@gmail.com>

slasher/service/src/service.rs

@@ -19,7 +19,6 @@ use state_processing::{
 use std::sync::mpsc::{sync_channel, Receiver, SyncSender, TrySendError};
 use std::sync::Arc;
 use task_executor::TaskExecutor;
-use tokio::stream::StreamExt;
 use tokio::sync::mpsc::UnboundedSender;
 use tokio::time::{interval_at, Duration, Instant};
 use types::{AttesterSlashing, Epoch, EthSpec, ProposerSlashing};
@@ -83,7 +82,8 @@ impl<T: BeaconChainTypes> SlasherService<T> {
         // https://github.com/sigp/lighthouse/issues/1861
         let mut interval = interval_at(Instant::now(), Duration::from_secs(update_period));
 
-        while interval.next().await.is_some() {
+        loop {
+            interval.tick().await;
             if let Some(current_slot) = beacon_chain.slot_clock.now() {
                 let current_epoch = current_slot.epoch(T::EthSpec::slots_per_epoch());
                 if let Err(TrySendError::Disconnected(_)) = notif_sender.try_send(current_epoch) {