Bump tokio-core from 0.1.17 to 0.1.18

Bumps [tokio-core](https://github.com/tokio-rs/tokio-core) from 0.1.17 to 0.1.18.
- [Release notes](https://github.com/tokio-rs/tokio-core/releases)
- [Commits](https://github.com/tokio-rs/tokio-core/commits)

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

Cargo.lock

@@ -3545,9 +3545,9 @@ dependencies = [
 
 [[package]]
 name = "tokio-core"
-version = "0.1.17"
+version = "0.1.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aeeffbbb94209023feaef3c196a41cbcdafa06b4a6f893f68779bb5e53796f71"
+checksum = "87b1395334443abca552f63d4f61d0486f12377c2ba8b368e523f89e828cffd4"
 dependencies = [
  "bytes 0.4.12",
  "futures 0.1.30",