Fixed rspec deprecations

- fixed rspec deprecation warning about non explicitly defined "should"-matcher
- removed rspec deprecation warning about "treat_symbols_as_metadata_keys_with_true_values".

>> Deprecation Warnings:
>> RSpec::Core::Configuration#treat_symbols_as_metadata_keys_with_true_values= is deprecated, it is now set to true as default and setting it to false has no effect.