function formatClosedIssues( closedIssues ) {
	var out = sectionStart( 'issues' );
	out += heading( 'Closed Issues', 3 );
	if ( closedIssues.length === 1 ) {
		out += 'This release closes the following issue:\n\n';
	} else {
		out += 'A total of ' + closedIssues.length + ' issues were closed in this release:\n\n';
	}
	out += map( closedIssues, formatIssue ).join( ', ' );
	out += sectionEnd( 'issues' );
	return out;
}
Formats closed issues as a comma-separated list.

@private
@param {ObjectArray} closedIssues - issue objects
@returns {string} formatted issues list