func (s *RepositoriesService) UpdateInvitation(ctx context.Context, repoID, invitationID int, permissions string) (*RepositoryInvitation, *Response, error) {
	opts := &struct {
		Permissions string `json:"permissions"`
	}{Permissions: permissions}
	u := fmt.Sprintf("repositories/%v/invitations/%v", repoID, invitationID)
	req, err := s.client.NewRequest("PATCH", u, opts)
	if err != nil {
		return nil, nil, err
	}
	req.Header.Set("Accept", mediaTypeRepositoryInvitationsPreview)
	invite := &RepositoryInvitation{}
	resp, err := s.client.Do(ctx, req, invite)
	return invite, resp, err
}
UpdateInvitation updates the permissions associated with a repository
invitation.

permissions represents the permissions that the associated user will have
on the repository. Possible values are: "read", "write", "admin".

GitHub API docs: https://developer.github.com/v3/repos/invitations/#update-a-repository-invitation
package github
import (
	"context"
	"fmt"
)
type RepositoryInvitation struct {
	ID      *int        `json:"id,omitempty"`
	Repo    *Repository `json:"repository,omitempty"`
	Invitee *User       `json:"invitee,omitempty"`
	Inviter *User       `json:"inviter,omitempty"`
	Permissions *string    `json:"permissions,omitempty"`
	CreatedAt   *Timestamp `json:"created_at,omitempty"`
	URL         *string    `json:"url,omitempty"`
	HTMLURL     *string    `json:"html_url,omitempty"`
}
func (s *RepositoriesService) ListInvitations(ctx context.Context, repoID int, opt *ListOptions) ([]*RepositoryInvitation, *Response, error) {
	u := fmt.Sprintf("repositories/%v/invitations", repoID)
	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
	}
	req.Header.Set("Accept", mediaTypeRepositoryInvitationsPreview)
	invites := []*RepositoryInvitation{}
	resp, err := s.client.Do(ctx, req, &invites)
	if err != nil {
		return nil, resp, err
	}
	return invites, resp, nil
}
func (s *RepositoriesService) DeleteInvitation(ctx context.Context, repoID, invitationID int) (*Response, error) {
	u := fmt.Sprintf("repositories/%v/invitations/%v", repoID, invitationID)
	req, err := s.client.NewRequest("DELETE", u, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", mediaTypeRepositoryInvitationsPreview)
	return s.client.Do(ctx, req, nil)
}