assignee_ids mismatch

Created by: rhd

Hi!

According to the edit issues api there should be an assignee_ids field. You code shows:

// UpdateIssueOptions represents the available UpdateIssue() options.
//
// GitLab API docs: https://docs.gitlab.com/ce/api/issues.html#edit-issues
type UpdateIssueOptions struct {
	Title            *string    `url:"title,omitempty" json:"title,omitempty"`
	Description      *string    `url:"description,omitempty" json:"description,omitempty"`
	Confidential     *bool      `url:"confidential,omitempty" json:"confidential,omitempty"`
	AssigneeID       *int       `url:"assignee_id,omitempty" json:"assignee_id,omitempty"`
	MilestoneID      *int       `url:"milestone_id,omitempty" json:"milestone_id,omitempty"`
	Labels           Labels     `url:"labels,comma,omitempty" json:"labels,omitempty"`
	StateEvent       *string    `url:"state_event,omitempty" json:"state_event,omitempty"`
	UpdatedAt        *time.Time `url:"updated_at,omitempty" json:"updated_at,omitempty"`
	DueDate          *ISOTime   `url:"due_date,omitempty" json:"due_date,omitempty"`
	DiscussionLocked *bool      `url:"discussion_locked,omitempty" json:"discussion_locked,omitempty"`
}

There appears to be a mismatch.

Thank you!