Upgrade holidays to 0.9.6

[fabaff]

Description:

Changes: https://github.com/dr-prodigy/python-holidays/blob/master/CHANGES

Example entry for configuration.yaml (if applicable):

binary_sensor:
  - platform: workday
    country: CH

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.

[MartinHjelmare]

Rebase to resolve this.

[fabaff]

Depends on https://github.com/dr-prodigy/python-holidays/issues/119

[ptdalen]

Component failed upon upgrade to 76.2 from 75.3

received the following errors

2018-08-21 19:34:11 ERROR (MainThread) [homeassistant.components.binary_sensor] Error while setting up platform workday
Traceback (most recent call last):
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/helpers/entity_platform.py", line 129, in _async_setup_platform
    SLOW_SETUP_MAX_WAIT, loop=hass.loop)
  File "/usr/lib/python3.6/asyncio/tasks.py", line 358, in wait_for
    return fut.result()
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/binary_sensor/workday.py", line 73, in setup_platform
    obj_holidays = getattr(holidays, country)(years=year)
AttributeError: module 'holidays' has no attribute 'US'

Reverted to previous version of component and it worked for me.