`be_true` and `be_false` are deprecated

Replace with `be true` and `be false` and make predicate return a
boolean.

> Methods that don't return a boolean, shouldn't end in a question mark.
-- https://github.com/bbatsov/ruby-style-guide#naming
Merge branch 'deprecation-warnings' into handle-quotation-marks-in-section-names

This should fix the build.

If this change isn't desired,
./spec/unit/puppet/provider/ini_setting/ruby_spec.rb:1044 could be
changed to:

```ruby
provider.exists?.should be_nil
```