cancel merge request http method use post not put

[fighter2011]

POST /projects/:id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds

[jmini]

This is the documentation:
https://docs.gitlab.com/ee/api/merge_requests.html#cancel-merge-when-pipeline-succeeds

This is our code:

gitlab4j-api/src/main/java/org/gitlab4j/api/MergeRequestApi.java

Lines 797 to 820 in ea9042e

	/**
	* Cancel merge when pipeline succeeds. If you don't have permissions to accept this merge request,
	* you'll get a 401. If the merge request is already merged or closed, you get 405 and
	* error message 'Method Not Allowed'. In case the merge request is not set to be merged when the
	* pipeline succeeds, you'll also get a 406 error.
	*
	* <p>NOTE: GitLab API V4 uses IID (internal ID), V3 uses ID to identify the merge request.</p>
	*
	* <pre><code>GitLab Endpoint: PUT /projects/:id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds</code></pre>
	*
	* @param projectIdOrPath the project in the form of an Long(ID), String(path), or Project instance
	* @param mergeRequestIid the internal ID of the merge request
	* @return the updated merge request
	* @throws GitLabApiException if any exception occurs
	*/
	public MergeRequest cancelMergeRequest(Object projectIdOrPath, Long mergeRequestIid) throws GitLabApiException {
	if (mergeRequestIid == null) {
	throw new RuntimeException("mergeRequestIid cannot be null");
	}
	Response response = put(Response.Status.OK, null, "projects", getProjectIdOrPath(projectIdOrPath), "merge_requests", mergeRequestIid, "cancel_merge_when_pipeline_succeeds");
	return (response.readEntity(MergeRequest.class));
	}