Check for a valid string on the regex transformer.  If not a valid string, then the value is ignored and the original record returned. (#136)

* Add Snowflake Extractor

* Move default value

* Add Snowflake extractor

Increment version

Update filter on hive_table_last_updated_extractor to use PARTITION_KEYS to filter out partitioned table (#109)

* Added Extractor for Athena metadata
Added Athena sample dag that uses Athena metadata extractor
Added Unit test for Athena metadata extractor

* Fixed flakey8 errors

* Fixed flakey8 error in the unit test

* Fixed typo changed Postgres to Athena

* Fix for ISSUE 98 - add example for usage data

* Issue 27 linting fixes.

* Update test_column_usage_model.py

* Update sample_data_loader.py

* Replace Threadpool to Pool

* Update

* Update

This is showing Airflow as the application because Amundsen already has
the Airflow icon but it could basically be any data transformation job
e.g SQL transforming from source dataset(s) to a resulting dataset
(Table).

* simplify elasticsearch databuilder workflow

* fix sample data loader

* Update default scope to be iterable for both py2 and py3

Encounter this issue( google.auth.exceptions.RefreshError: ('invalid_scope: h is not a valid audience string.', u'{\n  "error": "invalid_scope",\n  "error_description": "h is not a valid audience string."\n}')) which stackoverflow shows https://stackoverflow.com/questions/48332352/google-server-to-server-oauth-error.

* Update bigquery_metadata_extractor.py

* Update bigquery_metadata_extractor.py

* Update bigquery_metadata_extractor.py

* Update bigquery_metadata_extractor.py

* [AMD-149] Add updated timestamp into node and relation

* Update

* [AMD-120] Add relation pre-processor in Neo4jPublisher

* Update

* Added DeleteRelationPreprocessor

* Added DeleteRelationPreprocessor

* Update

* Update

* generalize ElasticsearchDocumentTransformer

* remove typo

* fix lint