Updated spark 2.3.x and spark 2.4.x versions to test against them. (#… #285

Job	Run time
matrix_prep	5s
publish_doc / matrix_prep	10s
build_coverage / matrix_prep	3s
build_coverage / build (3.0, test-uploadReport, release)	5m 27s
build_coverage / build (3.1, test-uploadReport, release)	5m 43s
build_coverage / build (3.2, test-uploadReport, release)	6m 39s
build_coverage / build (3.3, test-uploadReport, release)	6m 20s
build_coverage / build (3.4, test-uploadReport, release)	6m 25s
publish_doc / scaladoc_api (3.0, test-uploadReport, release)	3m 23s
publish_doc / scaladoc_api (3.1, test-uploadReport, release)	3m 21s
publish_doc / scaladoc_api (3.2, test-uploadReport, release)	3m 51s
publish_doc / scaladoc_api (3.3, test-uploadReport, release)	4m 16s
publish_doc / scaladoc_api (3.4, test-uploadReport, release)	3m 57s
publish_doc / generate_publish_mdoc	1m 54s
mvn_release (3.0, test-uploadReport, release)	4m 49s
mvn_release (3.1, test-uploadReport, release)	4m 33s
mvn_release (3.2, test-uploadReport, release)	6m 9s
mvn_release (3.3, test-uploadReport, release)	6m 21s
mvn_release (3.4, test-uploadReport, release)	6m 28s
	1h 19m 54s

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