Upgrade Mastodon.py to 1.4.2

[fabaff]

Description:

Changelog: https://github.com/halcy/Mastodon.py/blob/master/CHANGELOG.rst#v142

Example entry for configuration.yaml (if applicable):

notify:
  - name: mastodon
    platform: mastodon
    access_token: !secret mastodon_access_token
    client_id: !secret mastodon_client_id
    client_secret: !secret mastodon_client_secret

Data for Service call:

{
  "message": "The sun is {% if is_state('sun.sun', 'above_horizon') %}up{% else %}down{% endif %}! A Mastodon.py update for #homeassistant"
}

Result: https://mastodon.social/@fabaff/102128266606264495

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][dev-checklist]

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

• [The manifest file][manifest-docs] 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.