build(deps): bump futures-task from 0.3.5 to 0.3.21 in /examples (#96)

Bumps [futures-task](https://github.com/rust-lang/futures-rs) from 0.3.5 to 0.3.21.
- [Release notes](https://github.com/rust-lang/futures-rs/releases)
- [Changelog](https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/futures-rs/compare/0.3.5...0.3.21)

---
updated-dependencies:
- dependency-name: futures-task
  dependency-type: indirect
...

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/Cargo.lock

@@ -581,12 +581,9 @@ checksum = "3f2032893cb734c7a05d85ce0cc8b8c4075278e93b24b66f9de99d6eb0fa8acc"
 
 [[package]]
 name = "futures-task"
-version = "0.3.5"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bdb66b5f09e22019b1ab0830f7785bcea8e7a42148683f99214f73f8ec21a626"
-dependencies = [
- "once_cell",
-]
+checksum = "57c66a976bf5909d801bbef33416c41372779507e7a6b3a5e25e4749c58f776a"
 
 [[package]]
 name = "futures-util"
@@ -949,12 +946,6 @@ version = "0.20.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1ab52be62400ca80aa00285d25253d7f7c437b7375c4de678f5405d3afe82ca5"
 
-[[package]]
-name = "once_cell"
-version = "1.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b631f7e854af39a1739f401cf34a8a013dfe09eac4fa4dba91e9768bd28168d"
-
 [[package]]
 name = "parking_lot"
 version = "0.11.0"