#3864: Update Penner easing functions link (#3865)

site/content/tutorial/09-motion/01-tweened/text.md

@@ -28,7 +28,7 @@ Clicking the buttons causes the progress bar to animate to its new value. It's a
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-> The `svelte/easing` module contains the [Penner easing equations](http://robertpenner.com/easing/), or you can supply your own `p => t` function where `p` and `t` are both values between 0 and 1.
+> The `svelte/easing` module contains the [Penner easing equations](https://web.archive.org/web/20190805215728/http://robertpenner.com/easing/), or you can supply your own `p => t` function where `p` and `t` are both values between 0 and 1.
 
 The full set of options available to `tweened`:
 
@@ -37,4 +37,4 @@ The full set of options available to `tweened`:
 * `easing` — a `p => t` function
 * `interpolate` — a custom `(from, to) => t => value` function for interpolating between arbitrary values. By default, Svelte will interpolate between numbers, dates, and identically-shaped arrays and objects (as long as they only contain numbers and dates or other valid arrays and objects). If you want to interpolate (for example) colour strings or transformation matrices, supply a custom interpolator
 
-You can also pass these options to `progress.set` and `progress.update` as a second argument, in which case they will override the defaults. The `set` and `update` methods both return a promise that resolves when the tween completes.
+You can also pass these options to `progress.set` and `progress.update` as a second argument, in which case they will override the defaults. The `set` and `update` methods both return a promise that resolves when the tween completes.