Ignore needless_else clippy lint in test suite

    error: this else branch is empty
       --> tests/test_ensure.rs:177:42
        |
    177 |     let test = || Ok(ensure!(if false {} else {}.t(1) == 2));
        |                                          ^^^^^^^ help: you can remove it
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_else
        = note: `-D clippy::needless-else` implied by `-D clippy::all`

tests/test_ensure.rs

@@ -8,6 +8,7 @@
     clippy::let_and_return,
     clippy::let_underscore_untyped,
     clippy::match_bool,
+    clippy::needless_else,
     clippy::never_loop,
     clippy::overly_complex_bool_expr,
     clippy::redundant_closure_call,