Replace path-exists with fs.existsSync (#4731)

It's not deprecated anymore, see nodejs/node#8364

packages/babel-cli/src/babel/dir.js

@@ -1,5 +1,4 @@
 let outputFileSync = require("output-file-sync");
-let pathExists     = require("path-exists");
 let slash          = require("slash");
 let path           = require("path");
 let util           = require("./util");
@@ -45,7 +44,7 @@ module.exports = function (commander, filenames) {
   }
 
   function handle(filename) {
-    if (!pathExists.sync(filename)) return;
+    if (!fs.existsSync(filename)) return;
 
     let stat = fs.statSync(filename);
 

packages/babel-cli/src/babel/file.js

@@ -1,5 +1,4 @@
 let convertSourceMap = require("convert-source-map");
-let pathExists       = require("path-exists");
 let sourceMap        = require("source-map");
 let slash            = require("slash");
 let path             = require("path");
@@ -109,7 +108,7 @@ module.exports = function (commander, filenames, opts) {
     results = [];
 
     _.each(filenames, function (filename) {
-      if (!pathExists.sync(filename)) return;
+      if (!fs.existsSync(filename)) return;
 
       let stat = fs.statSync(filename);
       if (stat.isDirectory()) {

packages/babel-cli/src/babel/index.js

@@ -3,7 +3,7 @@
 
 require("babel-core");
 
-let pathExists = require("path-exists");
+let fs         = require("fs");
 let commander  = require("commander");
 let kebabCase  = require("lodash/kebabCase");
 let options    = require("babel-core").options;
@@ -70,7 +70,7 @@ let filenames = commander.args.reduce(function (globbed, input) {
 filenames = uniq(filenames);
 
 each(filenames, function (filename) {
-  if (!pathExists.sync(filename)) {
+  if (!fs.existsSync(filename)) {
     errors.push(filename + " doesn't exist");
   }
 });