Move grouped-queue require (#1190)

* Move grouped-queue require just before it will be used.

* Update lib/index.js

Co-Authored-By: Jacob Tomaw <jacob.tomaw@gmail.com>

Co-authored-by: Jacob Tomaw <jacob.tomaw@gmail.com>

lib/index.js

@@ -14,7 +14,6 @@ const runAsync = require('run-async');
 const through = require('through2');
 const FileEditor = require('mem-fs-editor');
 const createDebug = require('debug');
-const SubQueue = require('grouped-queue/lib/subqueue');
 const Environment = require('yeoman-environment');
 
 const Conflicter = require('./util/conflicter');
@@ -280,6 +279,15 @@ class Generator extends EventEmitter {
 
         // Backwards compatibilitiy with grouped-queue < 1.0.0
         if (!this.env.runLoop.addSubQueue) {
+          let SubQueue;
+          try {
+            SubQueue = require('grouped-queue/lib/subqueue');
+          } catch {
+            throw new Error(
+              "The running environment doesn't have the necessary features to run this generator. Update it and run again."
+            );
+          }
+
           this.env.runLoop.addSubQueue = function(name, before) {
             if (this.__queues__[name]) {
               // Sub-queue already exists