title: undefined function maps:to_json/1
body: <p>This is one of the things I learned from <code>Programming Erlang, 2nd Ed</code>, but doesn't seem to work on shell  </p>
  
  <pre><code>$ erl
  Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]
  
  Eshell V6.2  (abort with ^G)
  1&gt; Dic = #{b =&gt; 1, a =&gt; 2}.
  #{a =&gt; 2,b =&gt; 1}
  2&gt; maps:to_json(Dic).
  ** exception error: undefined function maps:to_json/1
  3&gt; 
  </code></pre>
  
  <p>What's wrong here?</p>