func (s *ActivityService) ListWatched(user string) ([]Repository, *Response, error) {
	var u string
	if user != "" {
		u = fmt.Sprintf("users/%v/subscriptions", user)
	} else {
		u = "user/subscriptions"
	}
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	watched := new([]Repository)
	resp, err := s.client.Do(req, watched)
	if err != nil {
		return nil, resp, err
	}
	return *watched, resp, err
}
ListWatched lists the repositories the specified user is watching.  Passing
the empty string will fetch watched repos for the authenticated user.

GitHub API Docs: https://developer.github.com/v3/activity/watching/#list-repositories-being-watched
package github
import "fmt"
type Subscription struct {
	Subscribed *bool      `json:"subscribed,omitempty"`
	Ignored    *bool      `json:"ignored,omitempty"`
	Reason     *string    `json:"reason,omitempty"`
	CreatedAt  *Timestamp `json:"created_at,omitempty"`
	URL        *string    `json:"url,omitempty"`
	RepositoryURL *string `json:"repository_url,omitempty"`
	ThreadURL *string `json:"thread_url,omitempty"`
}
func (s *ActivityService) ListWatchers(owner, repo string, opt *ListOptions) ([]User, *Response, error) {
	u := fmt.Sprintf("repos/%s/%s/subscribers", owner, repo)
	u, err := addOptions(u, opt)
	if err != nil {
		return nil, nil, err
	}
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	watchers := new([]User)
	resp, err := s.client.Do(req, watchers)
	if err != nil {
		return nil, resp, err
	}
	return *watchers, resp, err
}