title: ANTLR4 - Change token text
body: <p>Consider the following lexer rule:</p>
  <pre><code>TRUE : 'true' | 'TRUE' | '1';
  </code></pre>
  <p>I'd like all <code>TRUE</code> tokens to be converted to 'true'.</p>
  <p>I'm using <code>antlr4ts</code>. How do I do that?</p>