Merge pull request rails#23906 from schneems/schneems/puma-3-0

[close rails#23681] Use puma 3.0.0+

Author: schneems

railties/lib/rails/generators/app_base.rb

@@ -181,7 +181,7 @@ def database_gemfile_entry
       def webserver_gemfile_entry
         return [] if options[:skip_puma]
         comment = 'Use Puma as the app server'
-        GemfileEntry.new('puma', nil, comment)
+        GemfileEntry.new('puma', '~> 3.0', comment)
       end
 
       def include_all_railties?

railties/test/generators/app_generator_test.rb

@@ -366,6 +366,11 @@ def test_generator_without_skips
     end
   end
 
+  def test_generator_defaults_to_puma_version
+    run_generator [destination_root]
+    assert_gem "puma", "'~> 3.0'"
+  end
+
   def test_generator_if_skip_puma_is_given
     run_generator [destination_root, "--skip-puma"]
     assert_no_file "config/puma.rb"