langref: correct test runner path

Author: wyw

doc/langref.html.in

@@ -800,7 +800,7 @@
       </p>
       <aside>
         This documentation discusses the features of the default test runner as provided by the Zig Standard Library.
-        Its source code is located in <code class="file">lib/test_runner.zig</code>.
+        Its source code is located in <code class="file">lib/compiler/test_runner.zig</code>.
       </aside>
       <p>
         The shell output shown above displays two lines after the <kbd>zig test</kbd> command. These lines are