Add 'core' package (#136)

Author: rvanasa

src/components/Embed.tsx

@@ -2,6 +2,7 @@ import classNames from 'classnames';
 import copy from 'copy-to-clipboard';
 import mo from 'motoko/interpreter';
 import motokoBasePackage from 'motoko/packages/latest/base.json';
+import motokoCorePackage from 'motoko/packages/latest/core.json';
 import React, { useCallback, useEffect, useMemo, useState } from 'react';
 import { FaCode, FaLink, FaPause, FaPlay } from 'react-icons/fa';
 import useChangedState from '../hooks/useChangedState';
@@ -72,6 +73,7 @@ export default function Embed() {
     setLoading(true);
     mo.clearPackages();
     mo.loadPackage(motokoBasePackage);
+    mo.loadPackage(motokoCorePackage);
     mo.installPackages(Object.fromEntries(packages))
       .then(() => {
         setAutoRun(true);