ON THE ROAD: Ricky Gervais was spotted outside the Madewell Airstream on Thursday afternoon parked on Astor Place. Unfortunately, he decided not to check it out, but actress Elizabeth Olsen did. “My friend took me to Madewell when I first moved to New York and I was like, ‘This is the best place ever,’” said Olsen, who is about to leave for a two-month film shoot in Serbia. “I’m about to ship off to film a period piece. It’s a great affair story set in 1860s France, based on ‘Therese Raquin.’” She said it will be the first American film version of the novel.