Deprecate safe_level of `ERB.new` in Ruby 2.6
Deprecate safe_level of `ERB.new` in Ruby 2.6

see [Rails commmit](https://github.com/rails/rails/commit/e8be4f0891959afa1d6ca4510d1f9eb8e2887eb8).

recursecenter/sprockets,eileencodes/sprockets,rails/sprockets