code: func (s *GitService) GetCommit(ctx context.Context, owner string, repo string, sha string) (*Commit, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/git/commits/%v", owner, repo, sha)
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	c := new(Commit)
  	resp, err := s.client.Do(ctx, req, c)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return c, resp, nil
  }
docs: // GetCommit fetches the Commit object for a given SHA.
  //
  // GitHub API docs: https://developer.github.com/v3/git/commits/#get-a-commit