Change default easing to material design's "standard curve"

Was `ease`, now `cubic-bezier(0.4, 0.0, 0.2, 1)`
https://material.io/guidelines/motion/duration-easing.html#duration-easing-natural-easing-curves

_includes/options.html

@@ -6,7 +6,7 @@
 Shuffle.options = {
   group: Shuffle.ALL_ITEMS, // Initial filter group.
   speed: 250, // Transition/animation speed (milliseconds).
-  easing: 'ease', // CSS easing function to use.
+  easing: 'cubic-bezier(0.4, 0.0, 0.2, 1)', // CSS easing function to use.
   itemSelector: '*', // e.g. '.picture-item'.
   sizer: null, // Element or selector string. Use an element to determine the size of columns and gutters.
   gutterWidth: 0, // A static number or function that tells the plugin how wide the gutters between columns are (in pixels).

dist/shuffle.js

@@ -2140,7 +2140,7 @@ Shuffle.options = {
   speed: 250,
 
   // CSS easing function to use.
-  easing: 'ease',
+  easing: 'cubic-bezier(0.4, 0.0, 0.2, 1)',
 
   // e.g. '.picture-item'.
   itemSelector: '*',

src/shuffle.js

@@ -1121,7 +1121,7 @@ Shuffle.options = {
   speed: 250,
 
   // CSS easing function to use.
-  easing: 'ease',
+  easing: 'cubic-bezier(0.4, 0.0, 0.2, 1)',
 
   // e.g. '.picture-item'.
   itemSelector: '*',