addTeamMembership method
Invites a user to the specified team.
API docs: https://developer.github.com/v3/teams/members/#add-or-update-team-membership
Implementation
Future<TeamMembershipState> addTeamMembership(int teamId, String user) async {
final response = await github
.request('PUT', '/teams/$teamId/memberships/$user', statusCode: 200);
return TeamMembershipState(jsonDecode(response.body)['state']);
}