refactor snippets_list.js to use ES class syntax

app/assets/javascripts/snippets_list.js

-/* eslint-disable arrow-parens, no-param-reassign, space-before-function-paren, func-names, no-var, max-len */
-
-window.gl.SnippetsList = function() {
-  var $holder = $('.snippets-list-holder');
+function SnippetsList() {
+  const $holder = $('.snippets-list-holder');
 
   $holder.find('.pagination').on('ajax:success', (e, data) => {
     $holder.replaceWith(data.html);
   });
-};
+}
+
+window.gl.SnippetsList = SnippetsList;