Correctly mark a javadoc code snippet as such

Prevents it from rendering as a link (which would only result in a 404).

Partial gwtproject#8428

user/src/com/google/gwt/uibinder/attributeparsers/FieldReferenceConverter.java

@@ -65,7 +65,7 @@ public static class IllegalFieldReferenceException extends RuntimeException {
   interface Delegate {
     /**
      * Returns the types any parsed field references are expected to return.
-     * Multiple values indicates an overload. E.g., in <a href={...}> either a
+     * Multiple values indicates an overload. E.g., in <code>&lt;a href={...}&gt;</code> either a
      * String or a SafeUri is allowed.
      */
     JType[] getTypes();