Yield content length when streaming

This will be used by the download_endpoint Shrine plugin to set
Content-Length before it starts streaming.

Rakefile

@@ -4,4 +4,5 @@ require "rake/testtask"
 Rake::TestTask.new do |t|
   t.libs << "test"
   t.test_files = FileList["test/**/*_test.rb"]
+  t.warning = false
 end

lib/shrine/storage/fog.rb

@@ -28,7 +28,9 @@ def download(id)
       end
 
       def stream(id)
-        get(id) { |chunk| yield chunk }
+        get(id) do |chunk, _, content_length|
+          yield chunk, content_length
+        end
       end
 
       def open(id)

shrine-fog.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |gem|
   gem.name         = "shrine-fog"
-  gem.version      = "0.2.0"
+  gem.version      = "0.2.1"
 
   gem.required_ruby_version = ">= 2.1"