The Multiset code sample in TypeAdapterFactory's JavaDoc does not work

In Gson 2.8.5, the JavaDoc to `TypeAdapterFactory` presents a code sample of `MultisetTypeAdapterFactory`. However, this code sample does not work (instead of `MultisetTypeAdapterFactory`, `CollectionTypeAdapterFactory` is triggered). The problem is in these lines:
```
if (typeToken.getRawType() != Multiset.class || !(type instanceof ParameterizedType)) {
return null;
}

Type elementType = ((ParameterizedType) type).getActualTypeArguments()[0];
```

Instead, the following should be used (like in `CollectionTypeAdapterFactory`):
```
Class rawType = typeToken.getRawType();
if (!Multiset.class.isAssignableFrom(rawType)) {
return null;
}

Type elementType = $Gson$Types.getCollectionElementType(type, rawType);
```