Upgrade sqlalchemy to 1.2.6

[fabaff]

Description:

Changelog: http://docs.sqlalchemy.org/en/latest/changelog/changelog_12.html#change-1.2.6

Example entry for configuration.yaml (if applicable):

recorder:

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