add fields to UpdateMergeRequestOptions (#492)

merge_requests.go

@@ -512,6 +512,10 @@ type UpdateMergeRequestOptions struct {
 	Labels             Labels  `url:"labels,comma,omitempty" json:"labels,omitempty"`
 	MilestoneID        *int    `url:"milestone_id,omitempty" json:"milestone_id,omitempty"`
 	StateEvent         *string `url:"state_event,omitempty" json:"state_event,omitempty"`
+	RemoveSourceBranch *bool   `url:"remove_source_branch,omitempty" json:"remove_source_branch,omitempty"`
+	Squash             *bool   `url:"squash,omitempty" json:"squash,omitempty"`
+	DiscussionLocked   *bool   `url:"discussion_locked,omitempty" json:"discussion_locked,omitempty"`
+	AllowCollaboration *bool   `url:"allow_collaboration,omitempty" json:"allow_collaboration,omitempty"`
 }
 
 // UpdateMergeRequest updates an existing project milestone.