Gulp CLI fails with Windows Extended-Length Path

[charlespierce]

If Gulp is invoked with a Windows Extended-Length Path, then it immediately fails with an ENOENT error:

> node \\?\C:\Users\chuck\github\gulp-cli\bin\gulp.js -v
internal/fs/utils.js:220
    throw err;
    ^

Error: ENOENT: no such file or directory, scandir '\\?\C:\Users\chuck\github\gulp-cli/lib/versioned/'
    at Object.readdirSync (fs.js:854:3)
    at Object.<anonymous> (\\?\C:\Users\chuck\github\gulp-cli\index.js:31:17)
    at Module._compile (internal/modules/cjs/loader.js:956:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:973:10)
    at Module.load (internal/modules/cjs/loader.js:812:32)
    at Function.Module._load (internal/modules/cjs/loader.js:724:14)
    at Module.require (internal/modules/cjs/loader.js:849:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (\\?\C:\Users\chuck\github\gulp-cli\bin\gulp.js:5:1)
    at Module._compile (internal/modules/cjs/loader.js:956:30) {
  errno: -4058,
  syscall: 'scandir',
  code: 'ENOENT',
  path: '\\\\?\\C:\\Users\\chuck\\github\\gulp-cli/lib/versioned/'
}

This appears to be because a path is created using simple string concatenation, instead of path.join() in this file. Unlike normal paths, extended-length paths in Windows don't support / as a separator, so the resulting string is an invalid path when __dirname is an extended-length path.