Fix eslint no-unreachable in ES6

[MAILPOET-1085]

.eslintrc.es6.json

@@ -43,7 +43,6 @@
     "default-case": 0,
     "array-callback-return": 0,
     "consistent-return": 0,
-    "no-unreachable": 0,
     "import/no-unresolved": 0,
     "import/extensions": 0,
     "import/no-extraneous-dependencies": 0,

assets/js/src/form/fields/date.jsx

@@ -212,7 +212,6 @@ define([
               year={ this.state.year }
               placeholder={ this.props.field.year_placeholder }
             />);
-            break;
 
           case 'MM':
             return (<FormFieldDateMonth
@@ -224,7 +223,6 @@ define([
               monthNames={ monthNames }
               placeholder={ this.props.field.month_placeholder }
             />);
-            break;
 
           case 'DD':
             return (<FormFieldDateDay
@@ -235,7 +233,6 @@ define([
               day={ this.state.day }
               placeholder={ this.props.field.day_placeholder }
             />);
-            break;
         }
       });