Use compat instead of strict to follow json/yajl way. fix #1230

[repeatedly]

No description provided.

[repeatedly]

I can write messy test like below but it seems not unittest...

diff --git a/test/plugin/test_formatter_json.rb b/test/plugin/test_formatter_json.rb
index 5f80dd1..f073ea2 100644
--- a/test/plugin/test_formatter_json.rb
+++ b/test/plugin/test_formatter_json.rb
@@ -17,7 +17,7 @@ class JsonFormatterTest < ::Test::Unit::TestCase
   end

   def record
-    {'message' => 'awesome'}
+    {'message' => 'awesome', :message2 => :awesome2}
   end

   data('oj' => 'oj', 'yajl' => 'yajl')
@@ -27,4 +27,14 @@ class JsonFormatterTest < ::Test::Unit::TestCase

     assert_equal("#{Yajl.dump(record)}\n", formatted)
   end
+
+  def test_format_with_symbol_value
+    d = create_driver('json_parser' => 'oj')
+    require 'fluent/plugin/parser_json'
+    parser = Fluent::Plugin::JSONParser.new
+    parser.configure(config_element())
+    formatted = d.instance.format(tag, @time, record)
+
+    assert_equal("#{Yajl.dump(record)}\n", formatted)
+  end
 end

[tagomoris]

This default options are different from one in formatter_json.
You must make a common Oj default options as a constant, and share it in everywhere.

[repeatedly]

You must make a common Oj default options as a constant,

This is the trick but it seems acceptable.

[tagomoris]

LGTM.