Replace `include_class` with `contain_class`
Replace `include_class` with `contain_class`

`include_class` has been deprecated in favour of `contain_class` in rspec. When
a spec test is started and the spec configuration contains an `include_class`,
rspec still completes but warns of this deprecation.

This commit fixes the deprecation and means we no longer get warned about it.

alphagov/puppet-clamav