typo fix (#3963)

src/platforms/web/runtime/components/transition.js

@@ -22,7 +22,7 @@ export const transitionProps = {
 }
 
 // in case the child is also an abstract component, e.g. <keep-alive>
-// we want to recrusively retrieve the real component to be rendered
+// we want to recursively retrieve the real component to be rendered
 function getRealChild (vnode: ?VNode): ?VNode {
   const compOptions = vnode && vnode.componentOptions
   if (compOptions && compOptions.Ctor.options.abstract) {