Upgrade psutil to 5.5.0

[fabaff]

Description:

Changelog: https://github.com/giampaolo/psutil/blob/master/HISTORY.rst#550

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.

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 dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.