Add test with examples/primitives

.travis.yml

@@ -82,6 +82,7 @@ script:
   - pytest -v tests
   - labelme --help
   - labelme --version
+  - (cd examples/primitives && labelme_json_to_dataset primitives.json && rm -rf primitives_json)
   - (cd examples/tutorial && rm -rf apc2016_obj3_json && labelme_json_to_dataset apc2016_obj3.json && python load_label_png.py && git checkout -- .)
   - (cd examples/bbox_detection && rm -rf data_dataset_voc && ./labelme2voc.py labels.txt data_annotated data_dataset_voc && git checkout -- .)
   - (cd examples/semantic_segmentation && rm -rf data_dataset_voc && ./labelme2voc.py labels.txt data_annotated data_dataset_voc && git checkout -- .)