Gulp failing when using version()

Hello,

I was looking to implement versioning within my app. However, if I append .version() and run gulp an error is thrown:

 if (path.indexOf('./') == 0) {
                        ^

TypeError: Cannot read property 'indexOf' of undefined

Additionally, when I try the line:

    if (mix.inProduction()) {
        mix.version();
    }

An error is thrown that the function does not exist

if (mix.inProduction()) {
            ^

TypeError: mix.inProduction is not a function

And here is my package.json file:

{
  "private": true,
  "scripts": {
    "prod": "gulp --production",
    "dev": "gulp watch"
  },
  "devDependencies": {
    "bootstrap-sass": "^3.3.7",
    "gulp": "^3.9.1",
    "jquery": "^3.3.1",
    "laravel-elixir": "^6.0.0-18",
    "laravel-elixir-vue": "^0.1.4",
    "laravel-elixir-vue-2": "^0.3.0",
    "laravel-elixir-webpack-official": "^1.0.2",
    "laravel-mix": "^2.0",
    "lodash": "^4.17.10",
    "vue": "^2.5.16",
    "vue-resource": "^1.5.1"
  },
  "dependencies": {
    "@fortawesome/fontawesome": "^1.1.8",
    "@fortawesome/fontawesome-free-brands": "^5.0.13",
    "@fortawesome/fontawesome-pro-light": "^5.0.13",
    "@fortawesome/fontawesome-pro-regular": "^5.0.13",
    "@fortawesome/fontawesome-pro-solid": "^5.0.13",
    "gulp.spritesmith": "^6.9.0",
    "inputmask": "^4.0.0",
    "overhang": "^1.0.5",
    "sweetalert": "^2.1.0",
    "trip.js": "^3.3.3",
    "v-tooltip": "^2.0.0-rc.33",
    "vee-validate": "^2.0.9",
    "vue-cookie": "^1.1.4",
    "vue-inputmask": "^0.1.2"
  }
}