Log Message:
Update ruby-rspec-core to 3.4.3.

### Development
[Full Changelog](http://github.com/rspec/rspec-core/compare/v3.4.3...3-4-maintenance)

### 3.4.3 / 2016-02-19
[Full Changelog](http://github.com/rspec/rspec-core/compare/v3.4.2...3.4.3)

Bug Fixes:

* Prevent a `TypeError` from occuring when running via the rake task when
  Ruby crashes. (Patrik Wenger, #2161)
* Only consider example and group declaration lines from a specific file
  when applying line number filtering, instead of considering all
  declaration lines from all spec files. (Myron Marston, #2170)
* Fix failure snippet extraction so that snippets that contain `do-end` style
  block and end with `end`-only line can be extracted properly.
  (Yuji Nakayama, #2173)