Support RSpec3

My workaround for rspec 3.

Use `RSpec::Core::Runner` instead of `RSpec::Core::CommandLine`:

 [Merge RSpec::Core::CommandLine (never formally declared public) into RSpec::Core::Runner. (Myron Marston)](https://github.com/rspec/rspec-core/blob/master/Changelog.md#300rc1--2014-05-18)

Use `RSpec::Core::World#reset` and `RSpec::Core::Configuration#reset` which currently private api:
- [rspec-core/lib/rspec/core/world.rb at v3.0.3 · rspec/rspec-core](https://github.com/rspec/rspec-core/blob/v3.0.3/lib/rspec/core/world.rb#L48,L54)
- [rspec-core/lib/rspec/core/configuration.rb at v3.0.3 · rspec/rspec-core](https://github.com/rspec/rspec-core/blob/v3.0.3/lib/rspec/core/configuration.rb#L315,L320)

Use `config.color` instead of `config.color_enabled`:

[Remove color_enabled as an alias of color. (Jon Rowe)](https://github.com/rspec/rspec-core/blob/v3.0.3/Changelog.md#300rc1--2014-05-18)
Shouldn't this `end` be right after the `::RSpec.reset` line?
i.e. The config_cache block should be exectued for version 2 and 3