updating readme
updating readme

couldn't locate `"com.holdenkarau" %% "spark-testing-base" % "3.0.0_0.14.0" % "test"` in maven so I just updated it testing base version in the readme
holdenk/spark-testing-base,holdenk/spark-testing-base,holdenk/spark-testing-base,holdenk/spark-testing-base