Update index.html

out/guide/plugins/index.html

@@ -173,7 +173,7 @@ <h3 id="basic-assertion">Basic Assertion</h3>
 the assertion failed and the first error message will be thrown as part of a <code>chai.AssertionError</code>.
 Conversely, if the language chain was negated, it will consider <code>false</code> a pass and <code>true</code> a failure. 
 The second error message will be included in the thrown error instead.</p>
-<p>In all, the <code>assert</code> method accepts five arguments:</p>
+<p>In all, the <code>assert</code> method accepts six arguments:</p>
 <ol>
 <li>a boolean (result of a truth test)</li>
 <li>a string error message to be used if the first argument is <code>false</code></li>