Merge bitcoindevkit/bdk#738: Fix docs.rs features

3451d1c12e4271b6067ff246d095eb9fb1ca3bd5 Fix docs.rs features (Alekos Filini)

Pull request description:

  ### Description

  Fix docs.rs features

  ### 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 added tests for the new feature
  * [ ] I've added docs for the new feature
  * [ ] I've updated `CHANGELOG.md`

ACKs for top commit:
  danielabrozzoni:
    utACK 3451d1c12e4271b6067ff246d095eb9fb1ca3bd5
  notmandatory:
    ACK 3451d1c12e4271b6067ff246d095eb9fb1ca3bd5

Tree-SHA512: 96dc4f816b21cf20fc2828dcfd56865f3f9add8e4aa643205879c810d09e6f2e73d6643061bf3ca98145b37e726907dedd31a145f92d6646c172a43ae2285aa8

diff --cc Cargo.toml
Simple merge