Merge bitcoindevkit/bdk#550: Pin tokio version to ~1.14

b04bb590f385db349f8dc70cc169674b530c4205 Pin tokio version to ~1.14 (Steve Myers)

Pull request description:

  ### Description

  The `tokio` project recently changed their MSRV to `1.49.0`. This PR will pin the `tokio` dependency version to `~1.14` which is prior to their MSRV increase.

  ### Notes to the reviewers

  The LDK team took this approach for their `tokio` dev-dependency, see https://github.com/lightningdevkit/rust-lightning/pull/1315.

  As long as `tokio` backports bug fixes  to`1.14.x` releases this should be safe. If we need any new features we can revisit this decision.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [ ] I've updated `CHANGELOG.md`

ACKs for top commit:
  LLFourn:
    ACK b04bb590f385db349f8dc70cc169674b530c4205

Tree-SHA512: a44d61e0d644900837b5a99e0f2b9e5706cf9932f7430c3a2c8adbff37c82e4a6a545849fe031da748fcd8c8a70f5266d6974c5b6634b50af5eae148b9a26635