Upgrade libnacl to 1.6.1

[fabaff]

Description

• Make sure that libnacl runs correctly on the 1.0.15 release of libsodium

Example entry for configuration.yaml (if applicable):

device_tracker:
  - platform: owntracks
    secret: xyz

Checklist:

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 are only imported inside functions that use them ([example][ex-import]).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass