Use MR title as merge commit message (#15)

Author: pepakriz

src/GitlabApi.ts

@@ -23,6 +23,7 @@ export enum MergeState {
 export interface MergeRequest {
 	id: number;
 	iid: number;
+	title: string;
 	author: {
 		id: number;
 	};

src/MergeRequestAcceptor.ts

@@ -212,6 +212,7 @@ export const acceptMergeRequest = async (gitlabApi: GitlabApi, mergeRequest: Mer
 			should_remove_source_branch: true,
 			merge_when_pipeline_succeeds: true,
 			sha: mergeRequestInfo.diff_refs.head_sha,
+			squash_commit_message: `${mergeRequest.title} (#${mergeRequest.iid})`,
 		});
 
 		if (response.status === 405) { // cannot be merged