Bump tokio from 0.2.19 to 0.2.20

Bumps [tokio](https://github.com/tokio-rs/tokio) from 0.2.19 to 0.2.20.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/compare/tokio-0.2.19...tokio-0.2.20)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Cargo.lock

@@ -1698,9 +1698,9 @@ dependencies = [
 
 [[package]]
 name = "tokio"
-version = "0.2.19"
+version = "0.2.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7d9c43f1bb96970e153bcbae39a65e249ccb942bd9d36dbdf086024920417c9c"
+checksum = "05c1d570eb1a36f0345a5ce9c6c6e665b70b73d11236912c0b477616aeec47b1"
 dependencies = [
  "bytes",
  "fnv",