Upgrade psutil to 5.6.7

[fabaff]

Description:

Changelog: https://github.com/giampaolo/psutil/blob/master/HISTORY.rst#567

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: systemmonitor
    resources:
      - type: disk_use_percent
        arg: /home
      - type: memory_free

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

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

• The manifest file has all fields filled out correctly. Update and include derived files by running python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.