Fix IE10 transitions

The IE10 transition event is only fired on custom IE event, not the native `transitionend`. Luckly, they are already mapped, but the IE prefix must be uppercase (see https://github.com/Modernizr/Modernizr/commit/1dd860db0c50b2cd9ed6f57db1dbcc1614fe3d21#diff-afb1f0296e755884a8db059dcc9b2e9dL1281 for example).