Auto merge of #4534 - rust-lang:renovate/futures-util-0.x, r=Turbo87

Update Rust crate futures-util to v0.3.21

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [futures-util](https://crates.io/crates/futures-util) | dependencies | patch | `=0.3.19` -> `=0.3.21` |

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Author: bors

Cargo.lock

@@ -56,7 +56,7 @@ diesel_migrations = { version = "=1.4.0", features = ["postgres"] }
 dotenv = "=0.15.0"
 flate2 = "=1.0.22"
 futures-channel = { version = "=0.3.21", default-features = false }
-futures-util = "=0.3.19"
+futures-util = "=0.3.21"
 hex = "=0.4.3"
 http = "=0.2.6"
 hyper = { version = "=0.14.16", features = ["client", "http1"] }