fix(module): handle readJSFiles for string param (#143)

Author: wagerfield

docs/modules/workbox.md

@@ -67,7 +67,7 @@ It is recommanded to test workbox using `nuxt build`/`nuxt start`. You can enabl
 
 ### `workboxExtensions`
 
-(String) Loads and inserts the contents of the specified file path into the service worker script before any call to `precacheAndRoute`. You may add as many extra calls as you want to this file.
+(String|String[]) Loads and inserts the contents of the specified file path into the service worker script before any call to `precacheAndRoute`. You may add as many extra calls as you want to these files.
 
 <!-- Precache -->
 
@@ -91,7 +91,7 @@ Workbox takes a lot of the heavy lifting out of precaching by simplifying the AP
 
 ### `cachingExtensions`
 
-(String) Loads and inserts the contents of the specified file path into the service worker script, below autogenerated calls to `workbox.precaching.*`. You may add as many extra calls as you want to this file.
+(String|String[]) Loads and inserts the contents of the specified file path into the service worker script, below autogenerated calls to `workbox.precaching.*`. You may add as many extra calls as you want to these files.
 
 ### `cleanupOutdatedCaches`
 
@@ -129,7 +129,7 @@ Workbox takes a lot of the heavy lifting out of precaching by simplifying the AP
 
 ### `routingExtensions`
 
-(String) Loads and inserts the contents of the specified file path into the service worker script, below autogenerated calls to `workbox.routing.*`. You may add as many extra calls as you want to this file.
+(String|String[]) Loads and inserts the contents of the specified file path into the service worker script, below autogenerated calls to `workbox.routing.*`. You may add as many extra calls as you want to these files.
 
 ### `assetsURLPattern`
 

packages/workbox/lib/utils.js

@@ -1,7 +1,7 @@
 const { readFileSync, existsSync } = require('fs')
 
 function readJSFiles (files) {
-  return Array.from(files)
+  return Array.from(Array.isArray(files) ? files : [files])
     .map(path => {
       path = this.nuxt.resolver.resolvePath(path)
       if (path && existsSync(path)) {