Avoid RSpec deprecation warnings due to `be_true/be_false`

Fixes these warnings:

    `be_false` is deprecated. Use `be_falsey` (for Ruby's conditional semantics)
    or `be false` (for exact `== false` equality) instead.

    `be_true` is deprecated. Use `be_truthy` (for Ruby's conditional semantics)
    or `be true` (for exact `== true` equality) instead.

Using rspec-expectations v2.99.2