Fix: Keep compatibility with node < 5

README.md

@@ -1,7 +1,7 @@
 # rollup-plugin-istanbul
 
 [![Build Status](https://travis-ci.org/artberri/rollup-plugin-istanbul.svg?branch=master)](https://travis-ci.org/artberri/rollup-plugin-istanbul)
-[![Code Climate](https://codeclimate.com/github/artberri/rollup-plugin-istanbul/badges/gpa.svg)](https://codeclimate.com/github/artberri/rollup-plugin-istanbul)
+[![Maintainability](https://api.codeclimate.com/v1/badges/ea3da2334fcbff2a07c8/maintainability)](https://codeclimate.com/github/artberri/rollup-plugin-istanbul/maintainability)
 [![Last version](https://img.shields.io/npm/v/rollup-plugin-istanbul.svg)](https://www.npmjs.com/package/rollup-plugin-istanbul)
 [![Total Downloads](https://img.shields.io/npm/dt/rollup-plugin-istanbul.svg)](https://www.npmjs.com/package/rollup-plugin-istanbul)
 [![Downloads Last Month](https://img.shields.io/npm/dm/rollup-plugin-istanbul.svg)](https://www.npmjs.com/package/rollup-plugin-istanbul)

test/test.js

@@ -1,6 +1,6 @@
-let assert = require('assert');
-let rollup = require('rollup');
-let istanbulPlugin = require( '..' );
+var assert = require('assert');
+var rollup = require('rollup');
+var istanbulPlugin = require( '..' );
 
 process.chdir( __dirname );
 
@@ -17,7 +17,7 @@ describe('rollup-plugin-istanbul', function () {
     }).then( function ( bundle ) {
       return bundle.generate({format: 'iife'});
     }).then(generated => {
-      let code = generated.code;
+      var code = generated.code;
       assert.ok(code.indexOf('coverage[path]') !== -1, code);
     });
   });
@@ -32,7 +32,7 @@ describe('rollup-plugin-istanbul', function () {
     }).then( function ( bundle ) {
       return bundle.generate({format: 'iife'});
     }).then(generated => {
-      let code = generated.code;
+      var code = generated.code;
       assert.ok(code.indexOf('fixtures/main.js') !== -1, code);
     });
   });