Get rid of ERB warning for Ruby 2.6+

Signed-off-by: Takashi Kokubun <[email protected]>

lib/fluent/command/plugin_config_formatter.rb

@@ -164,15 +164,27 @@ def dump_section_markdown(base_section, level = 0)
     params.each do |name, config|
       next if name == :section
       template_name = @compact ? "param.md-compact.erb" : "param.md.erb"
-      dumped << ERB.new(template_path(template_name).read, nil, "-").result(binding)
+      template = template_path(template_name).read
+      dumped <<
+        if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+          ERB.new(template, trim_mode: "-")
+        else
+          ERB.new(template, nil, "-")
+        end.result(binding)
     end
     dumped << "\n"
     sections.each do |section_name, sub_section|
       required = sub_section.delete(:required)
       multi = sub_section.delete(:multi)
       alias_name = sub_section.delete(:alias)
       sub_section.delete(:section)
-      dumped << ERB.new(template_path("section.md.erb").read, nil, "-").result(binding)
+      template = template_path("section.md.erb").read
+      dumped <<
+        if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+          ERB.new(template, trim_mode: "-")
+        else
+          ERB.new(template, nil, "-")
+        end.result(binding)
     end
     dumped
   end

lib/fluent/command/plugin_generator.rb

@@ -72,7 +72,12 @@ def template_file(filename)
 
   def template(source, dest)
     dest.dirname.mkpath
-    contents = ERB.new(source.read, nil, "-").result(binding)
+    contents =
+      if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+        ERB.new(source.read, trim_mode: "-")
+      else
+        ERB.new(source.read, nil, "-")
+      end.result(binding)
     label = create_label(dest, contents)
     puts "\t#{label} #{dest}"
     if label == "conflict"