Maple Leafs notebook: Quick-study McKenna wowing already

TORONTO — Gavin McKenna adapts as fast as he shifts directions. The leap in performance from the teenager’s first pre-season game to his second was so loud, you could hear it in the gasps from Wednesday’s Scotiabank Arena crowd, an impressive portion of which were already decked out in straight-off-the-rack No. 92 sweaters. Be it speed or confidence, rewind-worthy dangles or clever reads, McKenna’s improvement from Saturday to Wednesday was the talk of the barn. “I think we all saw that, didn’t we?” Toronto Maple Leafs coach Jim Hiller said. “It’s going to be a process for him to understand…