Fix integ test

Author: Ignacio Quintero

tests/integ/test_mxnet_train.py

@@ -81,7 +81,7 @@ def test_async_fit(sagemaker_session, mxnet_full_version):
         mx = MXNet(entry_point=script_path, role='SageMakerRole', py_version=PYTHON_VERSION,
                    train_instance_count=1, train_instance_type='ml.c4.xlarge',
                    sagemaker_session=sagemaker_session, framework_version=mxnet_full_version,
-                   distributions={'parameter_server': {'enabled': True}})
+                   distribution={'parameter_server': {'enabled': True}})
 
         train_input = mx.sagemaker_session.upload_data(path=os.path.join(data_path, 'train'),
                                                        key_prefix='integ-test-data/mxnet_mnist/train')