Add [:and_criteria][:commit_email] to check result

Provides the author's email address in the check result hash:

```sh
› bundle console     
Resolving dependencies...
>> checker = ContributionChecker::Checker.new \
?>   :access_token => "your token",
?>   :commit_url   => "https://github.com/git/git-scm.com/commit/f6b5cb6"
>> checker.check
=> {
  :contribution => true,
  :and_criteria => {
    :commit_in_valid_branch => true,
    :commit_in_last_year => true,
    :repo_not_a_fork => true,
    :commit_email_linked_to_user => true,
    :commit_email => "example@example.com"
  },
  :or_criteria => {
    :user_has_starred_repo => false,
    :user_can_push_to_repo => false,
    :user_is_repo_org_member => false,
    :user_has_fork_of_repo => true
  }
}
```