contrib: Bump Dockerfile.alpine to alpine:3.14.0.

[briancolecoinmetrics]

Alpine 3.10 is EOL, and 3.14 is current

All Submissions:

• Submission follows the Code Contribution Guidelines
• There are not any other open Pull Requests for the same update/change
• Commit messages are formatted according to Model Git Commit Messages - probably albeit mostly by not being long enough to format

(I have omitted the rest of the checklist because I'm not touching any Go code)

[davecgh]

Thanks for the PR.