Replace <code> with {@code} in javadoc

{@code foo} is shorter and easier to read and write than
<code>foo</code>, which is why it was introduced years ago in the
javadoc processor.  Make consistent use of it throughout the
documentation comments.

Change-Id: I59d428cb6c5015453629398b0697891b83c8e91d

gerrit-gwtdebug/src/main/java/com/google/gerrit/gwtdebug/GerritDebugLauncher.java

@@ -259,7 +259,7 @@ public class GerritDebugLauncher extends ServletContainerLauncher {
   protected final class MyWebAppContext extends WebAppContext {
     /**
      * Parent ClassLoader for the Jetty web app, which can only load JVM
-     * classes. We would just use <code>null</code> for the parent ClassLoader
+     * classes. We would just use {@code null} for the parent ClassLoader
      * except this makes Jetty unhappy.
      */
     private final ClassLoader bootStrapOnlyClassLoader =