gesture,internal/fling: fix rounding

The code tried to extract a rounded whole number of pixels while preserving the
fraction. However, it failed to converge for the value 0.5, rounded to 1,
leaving -0.5, rounded to -1, leaving 0.5 and so on.

Drop the cleverness and truncate the values instead.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

internal/fling/animation.go

@@ -85,7 +85,7 @@ func (f *Animation) Tick(now time.Time) int {
 	ekt := float32(math.Exp(float64(k) * t.Seconds()))
 	x := f.v0*ekt/k - f.v0/k
 	dist := x - f.x
-	idist := int(math.Round(float64(dist)))
+	idist := int(dist)
 	f.x += float32(idist)
 	// Solving for the velocity x'(t) gives us
 	//