Reland rusoto and tokio upgrade

This reverts commit 87dd4be.

The cause of the leak was that `Regex::new` leaked 2.5 MB of memory on
every build (in `parse_rustc_version`). Searching around I found
rust-lang/regex#742, which said this was a
regression in thread_local.  Updating thread_local to 1.1.3 fixed the
issue.

For future reference: I debugged the leak as follows.

1. Build the crate: `cargo build`
2. Run the daemon under massif without registry watching: `valgrind --tool=massif target/debug/cratesfyi daemon --registry-watcher disabled`
3. Add a whole bunch of crates to the queue: `for i in $(seq 1 100); do cargo run -q queue add serde 1.0.$i; done`
4. Stop the daemon with SIGINT when you get tired of waiting (I ran about 30 builds).
5. Run `massif-visualizer` on the generated file.

Here are the changes to Cargo.lock:

```
> cargo update -p docs-rs
    Updating crates.io index
    Removing arrayref v0.3.6
    Removing arrayvec v0.5.1
      Adding attohttpc v0.16.3
    Updating base64 v0.11.0 -> v0.13.0
    Removing blake2b_simd v0.5.10
      Adding bytes v1.0.1
    Removing constant_time_eq v0.1.5
    Updating core-foundation v0.7.0 -> v0.9.1
    Updating core-foundation-sys v0.7.0 -> v0.8.2
      Adding crypto-mac v0.10.0
    Removing dirs v2.0.2
      Adding dirs-next v2.0.0
    Removing dirs-sys v0.3.5
      Adding dirs-sys-next v0.1.2
      Adding form_urlencoded v1.0.1
      Adding getrandom v0.2.2
    Updating h2 v0.2.5 -> v0.3.1
      Adding hmac v0.10.1
    Updating http-body v0.3.1 -> v0.4.1
    Updating hyper v0.13.10 -> v0.14.4
    Updating hyper-tls v0.4.1 -> v0.5.0
      Adding ipnet v2.3.0
    Updating js-sys v0.3.39 -> v0.3.49
    Updating libc v0.2.74 -> v0.2.91
      Adding mio v0.7.11
    Removing mio-named-pipes v0.1.6
    Updating miow v0.3.3 -> v0.3.7
    Updating native-tls v0.2.4 -> v0.2.7
      Adding ntapi v0.3.4
    Updating once_cell v1.4.0 -> v1.7.2
    Removing pin-project v0.4.17
    Removing pin-project-internal v0.4.17
      Adding postgres v0.19.0
      Adding postgres-protocol v0.6.0
      Adding postgres-types v0.2.0
    Updating r2d2_postgres v0.16.0 -> v0.18.0
      Adding rand v0.8.3
      Adding rand_chacha v0.3.0
      Adding rand_core v0.6.2
      Adding rand_hc v0.3.0
      Adding redox_syscall v0.2.5
    Updating redox_users v0.3.4 -> v0.4.0
    Updating reqwest v0.10.6 -> v0.11.2
    Updating rusoto_core v0.45.0 -> v0.46.0
    Updating rusoto_credential v0.45.0 -> v0.46.0
    Updating rusoto_s3 v0.45.0 -> v0.46.0
    Updating rusoto_signature v0.45.0 -> v0.46.0
    Removing rust-argon2 v0.7.0
    Updating rustwide v0.11.0 -> v0.12.0
    Updating security-framework v0.4.4 -> v2.1.2
    Updating security-framework-sys v0.4.3 -> v2.1.1
    Updating serde_urlencoded v0.6.1 -> v0.7.0
    Updating socket2 v0.3.12 -> v0.3.19
      Adding tokio v1.4.0
    Updating tokio-macros v0.2.5 -> v1.1.0
      Adding tokio-native-tls v0.3.0
      Adding tokio-postgres v0.7.0
      Adding tokio-stream v0.1.5
    Removing tokio-tls v0.3.1
      Adding tokio-util v0.6.5
    Updating url v2.1.1 -> v2.2.1
      Adding wasi v0.10.2+wasi-snapshot-preview1
    Updating wasm-bindgen v0.2.62 -> v0.2.72
    Updating wasm-bindgen-backend v0.2.62 -> v0.2.72
    Updating wasm-bindgen-futures v0.4.12 -> v0.4.22
    Updating wasm-bindgen-macro v0.2.62 -> v0.2.72
    Updating wasm-bindgen-macro-support v0.2.62 -> v0.2.72
    Updating wasm-bindgen-shared v0.2.62 -> v0.2.72
      Adding wildmatch v1.1.0
```