Determine if git from prefix also and add .git suffix if not there.

[gitlost]

Currently a package is determined to be a git only if the .git extension is present.

If given a standard github url like https://github.com/wp-cli-test/repository-name (or its ssh equivalent) without the .git suffix then it should also determine it to be a git package and append the .git suffix automatically.