Enable Hash#compact_blank inside ActiveSupport::LogSubscriber

Using ActiveSupport::LogSubscriber#color inside a custom log subscriber
causes NoMethodError.

```ruby
require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "activesupport"
end

require "active_support"

class TestLogSubscriber < ActiveSupport::LogSubscriber
  attach_to :test

  def hi(event)
    info(color(event.payload[:message], GREEN))
  end

  private
    def log_exception(name, e)
      super
      raise e
    end
end

ActiveSupport::LogSubscriber.logger = ActiveSupport::Logger.new(STDOUT)
ActiveSupport::Notifications.instrument("hi.test", message: "Hello!")
```

```
/rails/activesupport/lib/active_support/log_subscriber.rb:193:in `mode_from': undefined method `compact_blank' for an instance of Hash (NoMethodError)

      modes = MODES.values_at(*options.compact_blank.keys)
                                      ^^^^^^^^^^^^^^
```

For what it's worth, I have encountered this while using kredis locally, like;

```
$ cd kredis
$ bin/console
irb(main):001> Kredis.string "mystring"
Could not log "meta.kredis" event. NoMethodError: undefined method `compact_blank' for an instance of Hash
```

Author: sato11

activesupport/lib/active_support/log_subscriber.rb

@@ -2,6 +2,7 @@
 
 require "active_support/core_ext/module/attribute_accessors"
 require "active_support/core_ext/class/attribute"
+require "active_support/core_ext/enumerable"
 require "active_support/subscriber"
 require "active_support/deprecation/proxy_wrappers"