Upgrade xmltodict to 0.11.0

[fabaff]

0.11.0

• Determine fileness by checking for read attr
• Add support for Python 3.6.
• Release as a universal wheel.
• Updated docs examples to use print function.
• unparse: pass short_empty_elements to XMLGenerator
• Added namespace support when unparsing.

Tested with the following configuration:

sensor:
  - platform: swiss_hydrological_data
    name: Aare
    station: 2135
  - platform: yr
    monitored_conditions:
      - temperature
      - pressure
      - humidity

[mention-bot]

@fabaff, thanks for your PR! By analyzing the history of the files in this pull request, we identified @balloob, @kellerza and @rmkraus to be potential reviewers.