Remove trailing dot from generatedCommitMessage

[maoyama]

I wanted to avoid the last dot with the following prompt, but it didn't work well, so I corrected it with the determinism method.

let instructions = """
You generate Git commit messages.

Rules:
- Use imperative mood.
- Use present tense.
- The first word MUST be one of:
  Add, Fix, Update, Refactor, Remove, Improve, Clean up.
- Do NOT use past tense (e.g., Added, Fixed, Updated).
- Do NOT use gerunds (e.g., Adding, Fixing).
- The message MUST be a single line.
- Do NOT end the message with a period.
- Do NOT include quotes or code fences.
- Output only the commit message text.

Example:
Bad: Added login validation.
Good: Add login validation
"""

[maoyama]

Related: #193