Modify TimeWithZone#as_json to return 3DP of sub-second accuracy by default,...

Modify TimeWithZone#as_json to return 3DP of sub-second accuracy by default, since it's allowed by the spec and is very useful.

activesupport/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Modify `TimeWithZone#as_json` to include 3 decimal places of sub-second accuracy
+    by default, which is optional as per the ISO8601 spec, but extremely useful. Also
+    the default behaviour of Date#toJSON() in recent versions of Chrome, Safari and
+    Firefox.
+
 *   Improve `String#squish` to handle Unicode whitespace. *Antoine Lyset*
 
 *   Standardise on `to_time` returning an instance of `Time` in the local system timezone

activesupport/lib/active_support/time_with_zone.rb

@@ -154,7 +154,7 @@ def xmlschema(fraction_digits = 0)
     #   # => "2005/02/01 15:15:10 +0000"
     def as_json(options = nil)
       if ActiveSupport::JSON::Encoding.use_standard_json_time_format
-        xmlschema
+        xmlschema(3)
       else
         %(#{time.strftime("%Y/%m/%d %H:%M:%S")} #{formatted_offset(false)})
       end

activesupport/test/core_ext/time_with_zone_test.rb

@@ -75,7 +75,7 @@ def test_to_json_with_use_standard_json_time_format_config_set_to_false
 
   def test_to_json_with_use_standard_json_time_format_config_set_to_true
     old, ActiveSupport.use_standard_json_time_format = ActiveSupport.use_standard_json_time_format, true
-    assert_equal "\"1999-12-31T19:00:00-05:00\"", ActiveSupport::JSON.encode(@twz)
+    assert_equal "\"1999-12-31T19:00:00.000-05:00\"", ActiveSupport::JSON.encode(@twz)
   ensure
     ActiveSupport.use_standard_json_time_format = old
   end