Former Rangers captain Barry Ferguson admits he had concerns about the arrival of Jack Butland but the goalkeeper’s stellar Scottish Premiership showings have won over an Ibrox icon who now places himself alongside some of the club’s greatest glovesmen. If ever there was a moment which epitomised the impact Jack Butland has made north of the border, it was this. Kilmarnock were already 1-0 up against Philippe Clement’s side in midweek and threatening a second, only a sprawling, point-blank stop from the England international preventing the hosts from doubling their lead. Inside four second-hal…