Bump tokio from 0.2.12 to 0.2.13

Bumps [tokio](https://github.com/tokio-rs/tokio) from 0.2.12 to 0.2.13.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/commits)

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

Cargo.lock

@@ -1663,9 +1663,9 @@ dependencies = [
 
 [[package]]
 name = "tokio"
-version = "0.2.12"
+version = "0.2.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b34bee1facdc352fba10c9c58b654e6ecb6a2250167772bf86071f7c5f2f5061"
+checksum = "0fa5e81d6bc4e67fe889d5783bd2a128ab2e0cfa487e0be16b6a8d177b101616"
 dependencies = [
  "bytes",
  "fnv",