upgrade graphql-tools to v6 (#6701)

* upgrade to v6

* remove old graphql-tools package

Co-authored-by: Antonio Davi Macedo Coelho de Castro <adavimacedo@gmail.com>

src/GraphQL/ParseGraphQLSchema.js

@@ -5,7 +5,8 @@ import {
   DocumentNode,
   GraphQLNamedType,
 } from 'graphql';
-import { mergeSchemas, SchemaDirectiveVisitor } from 'graphql-tools';
+import { stitchSchemas } from '@graphql-tools/stitch';
+import { SchemaDirectiveVisitor } from '@graphql-tools/utils';
 import requiredParameter from '../requiredParameter';
 import * as defaultGraphQLTypes from './loaders/defaultGraphQLTypes';
 import * as parseClassTypes from './loaders/parseClassTypes';
@@ -251,7 +252,7 @@ class ParseGraphQLSchema {
             }
           }
         );
-        this.graphQLSchema = mergeSchemas({
+        this.graphQLSchema = stitchSchemas({
           schemas: [
             this.graphQLSchemaDirectivesDefinitions,
             this.graphQLAutoSchema,
@@ -262,10 +263,10 @@ class ParseGraphQLSchema {
         this.graphQLSchema = await this.graphQLCustomTypeDefs({
           directivesDefinitionsSchema: this.graphQLSchemaDirectivesDefinitions,
           autoSchema: this.graphQLAutoSchema,
-          mergeSchemas,
+          stitchSchemas,
         });
       } else {
-        this.graphQLSchema = mergeSchemas({
+        this.graphQLSchema = stitchSchemas({
           schemas: [
             this.graphQLSchemaDirectivesDefinitions,
             this.graphQLAutoSchema,