Fix obvious typo: Parameters.AUTHORS should use setAuthors()

This is an obvious typo to fix. In content/Page.java, starting from line 381, was:

if (!jsonObj.isNull(RetrieveResponse.Parameter.AUTHORS)) {
                JSONObject jsonAuthors =
                        jsonObj.getJSONObject(RetrieveResponse.Parameter.AUTHORS);
                String[] authors = JSONUtils.getKeys(jsonAuthors);
                mPage.setTags(authors);
            }

It should be mPage.setAuthors(authors); instead.