Converted milestone_select.js to axios

app/assets/javascripts/milestone_select.js

@@ -2,6 +2,7 @@
 /* global Issuable */
 /* global ListMilestone */
 import _ from 'underscore';
+import axios from './lib/utils/axios_utils';
 import { timeFor } from './lib/utils/datetime_utility';
 
 export default class MilestoneSelect {
@@ -52,9 +53,8 @@ export default class MilestoneSelect {
       }
       return $dropdown.glDropdown({
         showMenuAbove: showMenuAbove,
-        data: (term, callback) => $.ajax({
-          url: milestonesUrl
-        }).done((data) => {
+        data: (term, callback) => axios.get(milestonesUrl)
+          .then(({ data }) => {
             const extraOptions = [];
             if (showAny) {
               extraOptions.push({
@@ -200,11 +200,8 @@ export default class MilestoneSelect {
             data[abilityName].milestone_id = selected != null ? selected : null;
             $loading.removeClass('hidden').fadeIn();
             $dropdown.trigger('loading.gl.dropdown');
-            return $.ajax({
-              type: 'PUT',
-              url: issueUpdateURL,
-              data: data
-            }).done((data) => {
+            return axios.put(issueUpdateURL, data)
+              .then(({ data }) => {
                 $dropdown.trigger('loaded.gl.dropdown');
                 $loading.fadeOut();
                 $selectBox.hide();