Updated postman-collection require to be limited to usage of it

lib/index.js

@@ -1,7 +1,9 @@
 var schemaToQuery = require('./assets/gql-generator').schemaToQuery,
   converter,
   util = require('./util'),
-  sdk = require('postman-collection'),
+  { Collection } = require('postman-collection/lib/collection/collection'),
+  { ItemGroup } = require('postman-collection/lib/collection/item-group'),
+  { Variable } = require('postman-collection/lib/collection/variable'),
   _ = require('lodash'),
   graphql = require('graphql');
 
@@ -227,7 +229,7 @@ converter = {
   convert: function (input, options, callback) {
     var gqlSchemaObj,
       data,
-      collection = new sdk.Collection(),
+      collection = new Collection(),
       analysis,
       queryCollection;
 
@@ -284,7 +286,7 @@ converter = {
       }
 
       _.forEach(queryCollection, (value, key) => {
-        var folder = new sdk.ItemGroup();
+        var folder = new ItemGroup();
         folder.name = key;
         _.forEach(value, (graphqlObj, name) => {
           var request = {},
@@ -303,7 +305,7 @@ converter = {
         collection.items.add(folder);
       });
 
-      collection.variables.add(new sdk.Variable({
+      collection.variables.add(new Variable({
         id: 'url',
         value: '',
         description: 'URL for the request.'