Capture a missed VC error (#2436)

## Issue Addressed

Related to #2430, #2394

## Proposed Changes

As per https://github.com/sigp/lighthouse/issues/2430#issuecomment-875323615, ensure that the `ProductionValidatorClient::new` error raises a log and shuts down the VC. Also, I implemened `spawn_ignoring_error`, as per @michaelsproul's suggestion in https://github.com/sigp/lighthouse/pull/2436#issuecomment-876084419.

I got unlucky and CI picked up a [new rustsec vuln](https://rustsec.org/advisories/RUSTSEC-2021-0072). To fix this, I had to update the following crates:

- `tokio`
- `web3`
- `tokio-compat-02`

## Additional Info

NA

validator_client/src/attestation_service.rs

@@ -5,7 +5,6 @@ use crate::{
     validator_store::ValidatorStore,
 };
 use environment::RuntimeContext;
-use futures::future::FutureExt;
 use slog::{crit, error, info, trace};
 use slot_clock::SlotClock;
 use std::collections::HashMap;
@@ -205,15 +204,13 @@ impl<T: SlotClock + 'static, E: EthSpec> AttestationService<T, E> {
             .into_iter()
             .for_each(|(committee_index, validator_duties)| {
                 // Spawn a separate task for each attestation.
-                self.inner.context.executor.spawn(
-                    self.clone()
-                        .publish_attestations_and_aggregates(
-                            slot,
-                            committee_index,
-                            validator_duties,
-                            aggregate_production_instant,
-                        )
-                        .map(|_| ()),
+                self.inner.context.executor.spawn_ignoring_error(
+                    self.clone().publish_attestations_and_aggregates(
+                        slot,
+                        committee_index,
+                        validator_duties,
+                        aggregate_production_instant,
+                    ),
                     "attestation publish",
                 );
             });