Don't strip microseconds in JSON output. (#4256)

Author: tomchristie

rest_framework/utils/encoders.py

@@ -28,8 +28,6 @@ def default(self, obj):
             return force_text(obj)
         elif isinstance(obj, datetime.datetime):
             representation = obj.isoformat()
-            if obj.microsecond:
-                representation = representation[:23] + representation[26:]
             if representation.endswith('+00:00'):
                 representation = representation[:-6] + 'Z'
             return representation