Fix support for rspec-expectations 3.8.5+

[pirj]

This change adds value expectation support to RSpec's built-in raise_error matcher that is quite often used in projects using rspec-puppet, e.g.:

subject(:catalogue) { lambda { load_catalogue } }
it { is_expected.to raise_error Puppet::Error }

Also, since block matchers are more strict by default and don't accept value targets (defined as lambdas), this change adds an indicator that built-in rspec-puppet matchers do support value expectations as well as block expectations. This means that both:

it { expect(catalogue).to contain_file('README') }
it { expect { catalogue }.to contain_file('README') }

will work.

I'm not 100% certain this will work. Tested with https://github.com/voxpupuli/puppet-cassandra.
Appreciate if you can point out.

cc @alexjfisher @cyberious do you mind testing this against some of the projects depending on rspec-puppet that you maintain?

Related:
RSpec issue regarding the removal of implicit block syntax in a patch version rspec/rspec-expectations#1134
RSpec pull request with the removal rspec/rspec-expectations#1125
https://blog.rubystyle.guide/rspec/2019/07/17/rspec-implicit-block-syntax.html
rubocop/rspec-style-guide#76

[coveralls]

Coverage decreased (-0.4%) to 85.5% when pulling 97267a2 on pirj:pin-rspec-expectations into 85a0d71 on rodjek:master.

[rodjek]

Thanks so much @pirj! I've run this change against a bunch of modules and it looks good :)

[pirj]

Awesome, thank you!