Update to eslint 6

This updates eslint and related plugins to the next major version so
that we can make use of new features.

.eslintrc.yml

@@ -48,8 +48,10 @@ rules:
   no-jquery/no-serialize: error
   promise/always-return: off
   promise/no-callback-in-promise: off
+  # Make update to eslint@6 smoother:
+  prefer-object-spread: off
 overrides:
-  files:
-    - '**/spec/**/*'
-  rules:
-    "@gitlab/i18n/no-non-i18n-strings": off
+  - files:
+      - '**/spec/**/*'
+    rules:
+      "@gitlab/i18n/no-non-i18n-strings": off

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 */
 

package.json

@@ -146,7 +146,7 @@
   },
   "devDependencies": {
     "@babel/plugin-transform-modules-commonjs": "^7.5.0",
-    "@gitlab/eslint-config": "^2.1.2",
+    "@gitlab/eslint-config": "^3.0.0",
     "@vue/test-utils": "^1.0.0-beta.30",
     "axios-mock-adapter": "^1.15.0",
     "babel-jest": "^24.1.0",
@@ -157,10 +157,10 @@
     "commander": "^2.18.0",
     "custom-jquery-matchers": "^2.1.0",
     "docdash": "^1.0.2",
-    "eslint": "~5.9.0",
+    "eslint": "^6.8.0",
     "eslint-import-resolver-jest": "^2.1.1",
-    "eslint-import-resolver-webpack": "^0.10.1",
-    "eslint-plugin-jasmine": "^2.10.1",
+    "eslint-import-resolver-webpack": "^0.12.1",
+    "eslint-plugin-jasmine": "^4.1.0",
     "eslint-plugin-jest": "^22.3.0",
     "eslint-plugin-no-jquery": "^2.3.0",
     "gettext-extractor": "^3.4.3",

spec/frontend/.eslintrc.yml

@@ -6,6 +6,12 @@ plugins:
 extends:
   - 'plugin:jest/recommended'
 settings:
+  # We have to teach eslint-plugin-import what node modules we use
+  # otherwise there is an error when it tries to resolve them
+  import/core-modules:
+    - events
+    - fs
+    - path
   import/resolver:
     jest:
       jestConfigFile: 'jest.config.js'

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();