fix lint issues

index.js

@@ -1,8 +1,10 @@
 'use strict';
 
 const SchemaPack = require('./lib/schemapack.js').SchemaPack,
+  async = require('async'),
+  parse = require('./lib/parse.js'),
 
-// options for oas-resolver
+  // options for oas-resolver
   OasResolverOptions = {
     resolve: true, // Resolve external references
     jsonSchema: true // Treat $ref like JSON Schema and convert to OpenAPI Schema Objects

package.json

@@ -117,6 +117,7 @@
   },
   "dependencies": {
     "ajv": "6.10.2",
+    "async": "3.1.0",
     "commander": "2.3.0",
     "js-yaml": "3.13.1",
     "lodash": "4.17.13",