[Buttons] Fix FAB icon scale collapse timing (#1794)

The Floating Action Button's collapse animation timing function should
start at 40% and end at 100% (time), rather than starting at 0% and
ending at 20% (time).

Closes #1793

components/Buttons/src/MDCFloatingButton+Animation.m

@@ -196,9 +196,8 @@ - (void)collapse:(BOOL)animated completion:(void (^_Nullable)(void))completion {
                                                             [MDCFloatingButton collapseTransform])]
                    fromValue:nil
               timingFunction:[[CAMediaTimingFunction alloc]
-                                 initWithControlPoints:0.0f:0.0f:0.2f:1.0f]
-                    fillMode:kCAFillModeForwards
-                    duration:kMDCFloatingButtonExitIconDuration
+                                 initWithControlPoints:0.4f:0.0f:1.0f:1.0f]
+                    fillMode:kCAFillModeForwards duration:kMDCFloatingButtonExitIconDuration
                  beginOffset:kMDCFloatingButtonExitIconOffset];
     [self.imageView.layer addAnimation:iconScaleAnimation forKey:kMDCFloatingButtonTransformKey];