Fix the broken sample path in API (#1805)

* Fix the broken sample path in API

Related change b476a84

/hold
Need investigate why test doesn't catch it. 

/assign @numerology @hongye-sun

* Update sample_config.json

backend/src/apiserver/config/sample_config.json

@@ -2,12 +2,12 @@
   {
     "name":"[Sample] ML - XGBoost - Training with Confusion Matrix",
     "description":"A trainer that does end-to-end distributed training for XGBoost models. For source code, refer to https://github.com/kubeflow/pipelines/tree/master/samples/core/xgboost-spark",
-    "file":"/samples/core/xgboost-spark/xgboost-training-cm.py.tar.gz"
+    "file":"/samples/core/xgboost_training_cm/xgboost_training_cm.py.tar.gz"
   },
   {
     "name":"[Sample] ML - TFX - Taxi Tip Prediction Model Trainer",
     "description":"Example pipeline that does classification with model analysis based on a public tax cab BigQuery dataset. For source code, refer to https://github.com/kubeflow/pipelines/tree/master/samples/core/tfx",
-    "file":"/samples/core/tfx/taxi-cab-classification-pipeline.py.tar.gz"
+    "file":"/samples/core/tfx_cab_classification/tfx_cab_classification.py.tar.gz"
   },
   {
     "name":"[Sample] Basic - Sequential execution",
@@ -29,4 +29,4 @@
     "description":"A pipeline that downloads a message and prints it out. Exit Handler will run at the end. For source code, refer to https://github.com/kubeflow/pipelines/blob/master/samples/core/exit_handler/exit_handler.py",
     "file":"/samples/core/exit_handler/exit_handler.py.tar.gz"
   }
-]
+]