🐛 Don't load 'repl' unless needed

Git bisect revealed that process.stdout failed to initiate (and was replaced with a write stream that does nothing) when the 'repl' module was loaded. This commit moves `require('repl')` so that it is only loaded when the --interactive flag is present.

Fixes #5051

default_app/main.js

@@ -3,7 +3,6 @@ const {app, dialog, shell, Menu} = require('electron')
 const fs = require('fs')
 const Module = require('module')
 const path = require('path')
-const repl = require('repl')
 const url = require('url')
 
 // Parse command line options.
@@ -315,6 +314,7 @@ function startRepl () {
     return
   }
 
+  const repl = require('repl')
   repl.start('> ').on('exit', () => {
     process.exit(0)
   })

spec/node-spec.js

@@ -225,7 +225,7 @@ describe('node feature', function () {
       process.stdout.write('test')
     })
 
-    xit('should have isTTY defined', function () {
+    it('should have isTTY defined', function () {
       assert.equal(typeof process.stdout.isTTY, 'boolean')
     })
   })