Log Message:
devel/ruby-rspec-expectations: update to 3.7.0

### 3.7.0 / 2017-10-17
[Full Changelog](http://github.com/rspec/rspec-expectations/compare/v3.6.0...v3.7.0)

Enhancements:

* Improve compatibility with `--enable-frozen-string-literal` option
  on Ruby 2.3+. (Pat Allan, #997)