enhance shell scripting within changelog generator

[LucasLarson]

• use lowercase commit message
• replace gerund with imperative in commit message
• remove unnecessary --local from CI git config
• add end-of-options delimiter to git config entries
• use single quotes for user.name, user.email in git config
• prepend commands with command to avoid unexpected behavior
• apply shfmt -s -i 2
• use long flags when scripting