feat: upgrade js-yaml package (#403)

* feat: upgraded js-yaml package from v.3 to v.4 with YAML 1.2 support

* feat: removed timestamp type from YAML schema

packages/cli/src/utils.ts

@@ -2,7 +2,6 @@ import { basename, dirname, extname, join, resolve } from 'path';
 import { blue, gray, green, red, yellow } from 'colorette';
 import { performance } from "perf_hooks";
 import * as glob from 'glob-promise';
-import * as yaml from 'js-yaml';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as readline from 'readline';
@@ -13,6 +12,8 @@ import {
   LintConfig,
   ResolveError,
   YamlParseError,
+  parseYaml,
+  stringifyYaml
 } from '@redocly/openapi-core';
 import { Totals, outputExtensions } from './types';
 
@@ -87,7 +88,7 @@ export function dumpBundle(obj: any, format: BundleOutputFormat, dereference?: b
       throw e;
     }
   } else {
-    return yaml.safeDump(obj, {
+    return stringifyYaml(obj, {
       noRefs: !dereference,
     });
   }
@@ -131,11 +132,11 @@ export async function promptUser(query: string, hideUserInput = false): Promise<
 }
 
 export function readYaml(filename: string) {
-  return yaml.safeLoad(fs.readFileSync(filename, 'utf-8'), { filename });
+  return parseYaml(fs.readFileSync(filename, 'utf-8'), { filename });
 }
 
 export function writeYaml(data: any, filename: string, noRefs = false) {
-  const content = yaml.safeDump(data, { noRefs });
+  const content = stringifyYaml(data, { noRefs });
 
   if (process.env.NODE_ENV === 'test') {
     process.stderr.write(content);