add logic to prefer prebid modules over external modules in build process (#4124)

* add check in getModules helper function

* update logic based on feedback

* update node version of project

Author: jsnellbaker

.circleci/config.yml

@@ -7,7 +7,7 @@ jobs:
   build:
     docker:
       # specify the version you desire here
-      - image: circleci/node:7.10
+      - image: circleci/node:8.9.0
 
       # Specify service dependencies here if necessary
       # CircleCI maintains a library of pre-built images

README.md

@@ -66,7 +66,7 @@ module.exports = {
 }
 ```
 
-Or for Babel 6 and/or Node v8.6.0 and less:
+Or for Babel 6:
 ```javascript
             // you must manually install and specify the presets and plugins yourself
             options: {
@@ -112,7 +112,7 @@ prebid.requestBids({
     $ cd Prebid.js
     $ npm install
 
-*Note:* You need to have `NodeJS` 6.x or greater installed.
+*Note:* You need to have `NodeJS` 8.9.x or greater installed.
 
 *Note:* In the 1.24.0 release of Prebid.js we have transitioned to using gulp 4.0 from using gulp 3.9.1.  To compily with gulp's recommended setup for 4.0, you'll need to have `gulp-cli` installed globally prior to running the general `npm install`.  This shouldn't impact any other projects you may work on that use an earlier version of gulp in it's setup.
 

gulpHelpers.js

@@ -91,7 +91,10 @@ module.exports = {
     }
     return Object.assign(externalModules.reduce((memo, module) => {
       try {
-        var modulePath = require.resolve(module);
+        // prefer internal project modules before looking at project dependencies
+        var modulePath = require.resolve(module, {paths: ['./modules']});
+        if (modulePath === '') modulePath = require.resolve(module);
+
         memo[modulePath] = module;
       } catch (err) {
         // do something

package.json

@@ -21,7 +21,7 @@
   "author": "the prebid.js contributors",
   "license": "Apache-2.0",
   "engines": {
-    "node": ">=4.0"
+    "node": ">=8.9.0"
   },
   "devDependencies": {
     "@babel/core": "^7.2.2",