Bump iperf3 to 0.1.11

[frenck]

Description:

Bump iperf3 to 0.1.11
https://github.com/thiezn/iperf3-python/blob/master/HISTORY.rst#0111-2019-04-13

Related issue (if applicable): n/a

Pull request with documentation for home-assistant.io (if applicable): n/a

Example entry for configuration.yaml (if applicable):

iperf3:
  hosts:
    - host: iperf.he.net

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 user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

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.