chore: prepare Tokio v1.8.4 (#4237)

# 1.8.4 (November 15, 2021)

This release backports a bug fix from 1.13.1.

### Fixed

- sync: fix a data race between `oneshot::Sender::send` and awaiting a
  `oneshot::Receiver` when the oneshot has been closed ([#4226])

[#4226]: #4226

tokio/CHANGELOG.md

@@ -1,3 +1,14 @@
+# 1.8.4 (November 15, 2021)
+
+This release backports a bug fix from 1.13.1.
+
+### Fixed
+
+- sync: fix a data race between `oneshot::Sender::send` and awaiting a
+  `oneshot::Receiver` when the oneshot has been closed ([#4226])
+
+[#4226]: https://github.com/tokio-rs/tokio/pull/4226
+
 # 1.8.3 (July 26, 2021)
 
 This release backports two fixes from 1.9.0

tokio/Cargo.toml

@@ -7,12 +7,12 @@ name = "tokio"
 #   - README.md
 # - Update CHANGELOG.md.
 # - Create "v1.0.x" git tag.
-version = "1.8.3"
+version = "1.8.4"
 edition = "2018"
 authors = ["Tokio Contributors <team@tokio.rs>"]
 license = "MIT"
 readme = "README.md"
-documentation = "https://docs.rs/tokio/1.8.3/tokio/"
+documentation = "https://docs.rs/tokio/1.8.4/tokio/"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
 description = """