Color code output based on semver

[marccampbell]

Today the plugin shows an image red if it's > 3 versions out of date, yellow if 1 or 2, and green if up to date. For semver tags, we should rely on the semver contract, and show red if it's a major version (or more) outdated, yellow if it's 1 or more minor versions or patches outdated, and green if it's completely current