srfi-64.html: Standardize 'test-approximate' definition format.

* srfi-64.html (Simple test-cases) <test-approximate>: Wrap arguments
in 'var' tags.

Author: apteryks

srfi-64.html

@@ -171,7 +171,7 @@ <h4>Simple test-cases</h4>
 <p>For testing approximate equality of inexact reals
 we can use <code>test-approximate</code>:</p>
 <pre>
-(<b>test-approximate</b> [test-name] expected test-expr error)
+(<b>test-approximate</b> [<var>test-name</var>] <var>expected</var> <var>test-expr</var> <var>error</var>)
 </pre>
 <p>
 This is equivalent to (except that each argument is only evaluated once):</p>