Fix new eslint failures from major upgrade

app/assets/javascripts/due_date_select.js

+/* eslint-disable max-classes-per-file */
 import $ from 'jquery';
 import Pikaday from 'pikaday';
 import dateFormat from 'dateformat';

app/assets/javascripts/gl_dropdown.js

-/* eslint-disable  one-var, consistent-return */
+/* eslint-disable max-classes-per-file, one-var, consistent-return */
 
 import $ from 'jquery';
 import _ from 'underscore';

app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_failed_to_merge.vue

@@ -61,7 +61,7 @@ export default {
       eventHub.$emit('EnablePolling');
     },
     updateTimer() {
-      this.timer = this.timer - 1;
+      this.timer -= 1;
 
       if (this.timer === 0) {
         this.refresh();

ee/app/assets/javascripts/design_management/components/design_notes/design_discussion.vue

@@ -113,7 +113,7 @@ export default {
         />
         <apollo-mutation
           v-else
-          v-slot="{ mutate, loading, error }"
+          v-slot="{ mutate, loading }"
           :mutation="$options.createNoteMutation"
           :variables="{
             input: mutationPayload,

ee/app/assets/javascripts/group_member_contributions/store/group_member_store.js

@@ -43,7 +43,7 @@ export default class GroupMemberStore {
   sortMembers(sortByColumn) {
     if (sortByColumn) {
       this.state.currentSortedColumn = sortByColumn;
-      this.state.sortOrders[sortByColumn] = this.state.sortOrders[sortByColumn] * -1;
+      this.state.sortOrders[sortByColumn] *= -1;
 
       const currentColumnOrder = this.state.sortOrders[sortByColumn] || 1;
       const members = this.state.members.slice().sort((a, b) => {

ee/app/assets/javascripts/jira_connect.js

-/* eslint-disable func-names, prefer-arrow-callback, no-var, no-alert */
+/* eslint-disable func-names, no-var, no-alert */
 /* global $ */
 /* global AP */
 

spec/frontend/gl_field_errors_spec.js

-/* eslint-disable arrow-body-style */
-
 import $ from 'jquery';
 import GlFieldErrors from '~/gl_field_errors';
 

spec/frontend/vue_shared/components/issue/issue_assignees_spec.js

@@ -18,7 +18,7 @@ describe('IssueAssigneesComponent', () => {
         ...props,
       },
     });
-    vm = wrapper.vm; // eslint-disable-line
+    vm = wrapper.vm;
   };
 
   const findTooltipText = () => wrapper.find('.js-assignee-tooltip').text();