Set pattern parameter thorugh `pattern=`

refs GH-143

If set `pattern` parameter through `patrern=`, will be used preferentially **option parameter** even if `RSpec.configure.pattern=`

- https://github.com/rspec/rspec-core/blob/v3.0.4/lib/rspec/core/configuration.rb#L187
- [RSpec::Configuration.define_reader](https://github.com/rspec/rspec-core/blob/v3.0.4/lib/rspec/core/configuration.rb#L39-L44)
- https://github.com/rspec/rspec-core/blob/v3.0.4/lib/rspec/core/configuration.rb#L1304
- https://github.com/rspec/rspec-core/blob/v3.0.4/lib/rspec/core/configuration.rb#L1286

But, If append `pattern` parameter not through `pattern=`, will be used **option parameter + append parameter**

:cloud: `config.pattern <<` mean `@pattern <<`. 

So, problem of GH-143  occur. Example:

1. Set option in `.rspec`

    ```
    --pattern spec/{**/*_spec.rb,acceptance/**/*.feature}
    ```

    - This is set to [@peferred_options[:pattern]](https://github.com/rspec/rspec-core/blob/v3.0.4/lib/rspec/core/configuration.rb#L313)

1. Use [config.pattern <<]