Run instance_segmentation example on Travis

.travis.yml

@@ -96,6 +96,7 @@ script:
   - labelme --help
   - (cd examples/single_image && rm -rf apc2016_obj3_json && labelme_json_to_dataset apc2016_obj3.json && python load_label_png.py && git checkout -- .)
   - (cd examples/semantic_segmentation && rm -rf data_dataset_voc && ./labelme2voc.py labels.txt data_annotated data_dataset_voc && git checkout -- .)
+  - (cd examples/instance_segmentation && rm -rf data_dataset_voc && ./labelme2voc.py labels.txt data_annotated data_dataset_voc && git checkout -- .)
 
 branches:
   only: