Add eslint rule to require parentheses in arrow functions

[MAILPOET-2162]

assets/js/src/common/key_value_table.jsx

@@ -1,10 +1,10 @@
 import PropTypes from 'prop-types';
 import React from 'react';
 
-const KeyValueTable = props => (
+const KeyValueTable = (props) => (
   <table className="widefat fixed" style={{ maxWidth: props.max_width }}>
     <tbody>
-      {props.rows.map(row => (
+      {props.rows.map((row) => (
         <tr key={`row_${row.key}`}>
           <td className="row-title">{ row.key }</td>
           <td>{ row.value }</td>

assets/js/src/common/print_boolean.jsx

@@ -2,7 +2,7 @@ import PropTypes from 'prop-types';
 import React from 'react';
 import MailPoet from 'mailpoet';
 
-const PrintBoolean = props => (
+const PrintBoolean = (props) => (
   <span>
     {(props.children === true && props.truthy)
       || (props.children === false && props.falsy)

assets/js/src/common/stepped_progess_bar.jsx

@@ -8,7 +8,7 @@ const SteppedProgressBar = (props) => {
   return (
     <div className="mailpoet_stepped_progress_bar">
       {
-        [...Array(props.steps_count).keys()].map(step => (
+        [...Array(props.steps_count).keys()].map((step) => (
           <div
             className={`
               mailpoet_stepped_progress_bar_step ${(step < props.step ? 'active' : '')} ${(step === (props.step - 1) ? 'current' : '')}

assets/js/src/common/thumbnail.jsx

@@ -21,7 +21,7 @@ export const fromDom = async (element) => {
  * @param  {String}        url
  * @return {Promise<String>} DataURL of the generated image.
  */
-export const fromUrl = url => new Promise((resolve, reject) => {
+export const fromUrl = (url) => new Promise((resolve, reject) => {
   const iframe = document.createElement('iframe');
   const protocol = document.location.href.startsWith('https://') ? 'https:' : 'http:';
   iframe.src = protocol + url.replace(/^https?:/, '');
@@ -59,7 +59,7 @@ export const fromUrl = url => new Promise((resolve, reject) => {
  * @param  {Object}        data
  * @return {Promise<String>} DataURL of the generated image.
  */
-export const fromNewsletter = data => new Promise((resolve, reject) => {
+export const fromNewsletter = (data) => new Promise((resolve, reject) => {
   const json = data;
   if (!_.isUndefined(json.body)) {
     json.body = JSON.stringify(json.body);
@@ -69,7 +69,7 @@ export const fromNewsletter = data => new Promise((resolve, reject) => {
     endpoint: 'newsletters',
     action: 'showPreview',
     data: json,
-  }).done(response => fromUrl(response.meta.preview_url)
+  }).done((response) => fromUrl(response.meta.preview_url)
     .then(resolve)
-    .catch(reject)).fail(response => reject(response.errors));
+    .catch(reject)).fail((response) => reject(response.errors));
 });