message: Fix a typo in the comments.
diff: @@ -56,9 +56,9 @@ limitations under the License.
  //
  // To add values to feature_lists:
  // AppendFeatureValues({4.0},
  -// GetFeatureList("movie_ratings", &se)->Add());
  +// GetFeatureList("images", &se)->Add());
  // AppendFeatureValues({5.0, 3.0},
  -// GetFeatureList("movie_ratings", &se)->Add());
  +// GetFeatureList("images", &se)->Add());
  // This will create a feature list keyed as "images" with two features:
  // feature_lists {
  // feature_list {
  