Upgrade python-twitch-client to 0.6.0

[fabaff]

Description:

Changelog: https://github.com/tsifrer/python-twitch-client/blob/master/CHANGELOG.md#version-060---2018-09-10

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: twitch
    client_id: !secret twitch_api
    channels:
      - thijshs
      - danotage

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][ex-requir]).
• New or updated dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.