make sure all file names are using forward slashes

Author: jrainville

lib/core/file.js

@@ -7,7 +7,7 @@ const utils = require('../utils/utils');
 class File {
 
   constructor (options) {
-    this.filename = options.filename;
+    this.filename = options.filename.replace(/\\/g, '/');
     this.type = options.type;
     this.path = options.path;
     this.basedir = options.basedir;