Update ssd_inception_v3_pets.config (#7592)

research/object_detection/samples/configs/ssd_inception_v3_pets.config

-# SSD with Inception v2 configured for Oxford-IIIT Pets Dataset.
+# SSD with Inception v3 configured for Oxford-IIIT Pets Dataset.
 # Users should configure the fine_tune_checkpoint field in the train config as
 # well as the label_map_path and input_path fields in the train_input_reader and
 # eval_input_reader. Search for "PATH_TO_BE_CONFIGURED" to find the fields that