Update to 6.47

Upstream changes:
6.47  2016-02-19
  - Deprecated Mojo::Log::is_debug, Mojo::Log::is_error, Mojo::Log::is_info and
    Mojo::Log::is_warn in favor of Mojo::Log::is_level.
  - Added is_level method to Mojo::Log.
  - Fixed datetime_field helper to use the correct type attribute value.

(wen)