Require using arrow functions as callbacks

Signed-off-by: Rūdolfs Ošiņš <rudolfs@osins.org>

.eslintrc.json

@@ -97,7 +97,11 @@
     ],
     // Disallow Unused Variables.
     // https://eslint.org/docs/rules/no-unused-vars
-    "@typescript-eslint/no-unused-vars": ["error", { "argsIgnorePattern": "^_" }]
+    "@typescript-eslint/no-unused-vars": ["error", { "argsIgnorePattern": "^_" }],
+    // Require using arrow functions as callbacks.
+    // https://eslint.org/docs/rules/prefer-arrow-callback
+    "prefer-arrow-callback": "error"
+
   },
   "settings": {
     "svelte3/typescript": true

src/BlockTimer.spec.ts

@@ -4,7 +4,7 @@ import "@public/index.css";
 import type { EventType, Listener } from "@ethersproject/abstract-provider";
 
 
-describe('BlockTimer', function () {
+describe('BlockTimer', () => {
   it("increases correctly the loading bar", () => {
     let block = 1;
     const props = {

src/Error.spec.ts

@@ -3,7 +3,7 @@ import { render } from "@testing-library/svelte";
 import { Failure } from '@app/error';
 import "@public/index.css";
 
-describe('Error', function () {
+describe('Error', () => {
   it("should show passed in props", () => {
     render(Error, { props: {
       subtitle: "Subtitle of Modal",

src/NotFound.spec.ts

@@ -2,7 +2,7 @@ import NotFound from "./NotFound.svelte";
 import { render } from "@testing-library/svelte";
 import "@public/index.css";
 
-describe('NotFound', function () {
+describe('NotFound', () => {
   it("shows passed props correctly", () => {
     render(NotFound, {
       props: {

src/SeedAddress.spec.ts

@@ -2,7 +2,7 @@ import SeedAddress from "./SeedAddress.svelte";
 import { render } from "@testing-library/svelte";
 import "@public/index.css";
 
-describe('SeedAddress', function () {
+describe('SeedAddress', () => {
   it("shows the seed emoji and seed host", () => {
     render(SeedAddress, {
       props: {

src/base/projects/PeerSelector.spec.ts

@@ -13,7 +13,7 @@ const defaultProps = {
   ],
 };
 
-describe('Logic', function () {
+describe('Logic', () => {
   it("show delegate name and badge", () => {
     render(PeerSelector, {
       props: defaultProps