Fix overly match-happy sed commands

[jsf9k]

🗣 Description

This pull request tightens a few sed commands so that their regexes do not inadvertently match when they should not.

💭 Motivation and context

We saw in cisagov/postfix-docker#47 that the sed commands in the bump_version.sh script could inadvertently match the CC0 version in the README.md file. This change escapes the periods in the version before passing it on to sed so that they only match periods and not just any character.

🧪 Testing

I tested locally and verified that with these changes the situation that arose in cisagov/postfix-docker#47 does not occur.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.

[jsf9k]

This repo needs a lineage PR before the linting tasks can pass.