Raise minimum tested version to rustc 1.53
Raise minimum tested version to rustc 1.53

On 1.52:

    error[E0658]: or-patterns syntax is experimental
       --> tests/test_ensure.rs:187:22
        |
    187 |     let test = || Ok(ensure!(for true | false in iter::empty() {}.t(1) == 2));
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

dtolnay/anyhow