Fix consistent-return eslint rule in ES6 files

[MAILPOET-1139]

.eslintrc.es6.json

@@ -40,7 +40,6 @@
     "jsx-a11y/alt-text": 0,
     "func-names": 0,
     "object-shorthand": 0,
-    "consistent-return": 0,
     "import/extensions": 0,
     "import/no-extraneous-dependencies": 0,
     "camelcase": 0,

assets/js/src/help/system_status.jsx

@@ -42,7 +42,7 @@ function renderCronSection(data) {
 }
 
 function renderMSSSection(data) {
-  if (!data.mss.enabled) return;
+  if (!data.mss.enabled) return undefined;
 
   const status = data.mss.enabled.isReachable;
 

assets/js/src/newsletters/send/standard.jsx

@@ -217,7 +217,7 @@ define(
       },
       propagateChange: function () {
         if (this.props.onChange) {
-          return this.props.onChange({
+          this.props.onChange({
             target: {
               name: this.props.name || '',
               value: this.getDateTime(),

assets/js/src/newsletters/templates.jsx

@@ -57,6 +57,7 @@ const ImportTemplate = React.createClass({
     };
 
     reader.readAsText(file);
+    return true;
   },
   render: function () {
     return (

assets/js/src/subscribers/form.jsx

@@ -170,6 +170,7 @@ define(
           </p>
         );
       }
+      return undefined;
     };
 
     const afterFormContent = function () {