Revert "Add erubis to gemspec so that benchmark file can run"

This reverts commit 0349ae4.

Reason: The bundle in benchmark.rb fails now because the newest rails depends on erubi instead of erubis.
It'd be better to update our script to use erubi with rails 5.1+ rather than adding a new dependency.

CHANGELOG.md

@@ -2,7 +2,6 @@
 
 * Add constant for default options in `lib/haml/helpers/action_view_mods.rb` [#966](https://github.com/haml/haml/pull/966) (thanks [Dillon Welch](https://github.com/oniofchaos))
 * Performance/memory usage improvement in `lib/haml/buffer.rb` [#963](https://github.com/haml/haml/pull/963) (thanks [Dillon Welch](https://github.com/oniofchaos))
-* Add erubis to gemspec so that `benchmark.rb` works [#964](https://github.com/haml/haml/pull/964) (thanks [Dillon Welch](https://github.com/oniofchaos))
 
 ## 5.0.4
 

haml.gemspec

@@ -22,7 +22,6 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'temple', '>= 0.8.0'
   spec.add_dependency 'tilt'
 
-  spec.add_development_dependency 'erubis' # for benchmark.rb
   spec.add_development_dependency 'rails', '>= 4.0.0'
   spec.add_development_dependency 'rbench'
   spec.add_development_dependency 'minitest', '>= 4.0'