Log Message:
Update ruby-byebug to 9.1.0.

## 9.1.0 - 2016-08-22

### Added

* Better UI messages for breakpoint management.

### Fixed

* `where` command failing on instance_exec block stack frames.
* `restart` command crashing in certain cases because of a missing `require \ 
'English'` (#321, @akaneko3).
* `restart` command crashing when debugged script is not executable or has no \ 
shebang (#321, @akaneko3).

### Removed

* Ruby 2.0 and Ruby 2.1 official & unofficial support. Byebug no longer installs
  on these platforms.