types(showdown): fix header authors format
types(showdown): fix header authors format

borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,magny/DefinitelyTyped,mcliment/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,markogresak/DefinitelyTyped