RSpec::Core::ConfigurationOptions#options support for rspec-core 3.0.0.beta2. Fix #249

RSpec::Core::ConfigurationOptions#parse_options method was renamed to #options
in rspec-core v3.0.0.beta2 so call the first one only if it is available.
Merge pull request #250 from 907th/fix_249

RSpec::Core::ConfigurationOptions#options support for rspec-core 3.0.0.beta2. Fix #249