fix: user-agent is not string in logs

[denelvis]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• The PR has self-explained commits history.
• The code is mine, or it's from somewhere with an Apache-2.0 compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable, and I have tested it myself, to the best of my abilities.
• If the code introduces new classes, methods, I provide a valid use case for all of them.

Changes:

• Fix missed JSON.stringify(...) in patch: logger functionality #762.

[shpingalet007]

Quality checked.

@denelvis, please don't forgot to fill the checklist in PR. It is important for seniors to be able to understand the situation. Now I'll accept it, as I see that it's small, but next time I'll wait the checklist before merging. Thanks.

@zanhesl, the #762 wasn't checked well on logger before merge.