Update tokio to 1.0

[lsunsi]

It's a major first release which the whole ecosystem is supporting, so we should probably follow suit in order to provide better compatibility for web3 users.

I realise we can't 'just upgrade' due to underlying packages, so I'll make a list of packages that require tokio and can be upgraded and the ones that are blocking our upgrade.

Already updated

• hyper (v0.14)
• hyper-tls (v0.5)

Not updated

• async-native-tls (Update to Tokio 1.0 async-email/async-native-tls#26)
• hyper-proxy (Update to Tokio 1.0 tafia/hyper-proxy#19)

[smessmer]

hyper-proxy 0.9.0 and async-native-tls master now support tokio 1.0

[soulmachine]

bump

[tomusdrw]

@soulmachine the PR is pending in #454 but we're still waiting for async-native-tls to release new version to crates.io.