At the time of this commit that's slim v3.0.1.

That is, except for Ruby 1.8.7 installations. Slim dropped support[^0] for Ruby
1.8.7 in their 3.0.0 release. This commit allows Brakeman to move forward with
slim support on all supported later Ruby versions.

To do this accurately we must install an appropriate version of Slim by
inspecting `RUBY_VERSION` at install time. We do that by using the native
extensions hooks available as part of gem installs. Ours is modeled after an
example on GitHub[^1].

[^0]: https://github.com/slim-template/slim/blob/master/CHANGES#L12
[^1]: https://github.com/mmzyk/gem_dependency_example/tree/master/gem_dep_example

- Fix a few test related failures on 2.2.0.
- Allow default rubygems version to run (v2.4.5).

This reverts commit 5f788264.

at least for Travis satisfaction

closes #263

Should fix #247

it was for ActiveRecord

This fixes a conflict with the 'tomdoc' gem.

closes #164

closes #153

This commit handles the conversion of:
* headers
* overviews
* warning_overviews
* controller/view debug output
* errors

because the next RubyParser release is going to break a LOT of stuff.