code: @Override
      public INDArray randn(long rows, long columns, org.nd4j.linalg.api.rng.Random r) {
          return randn(new long[] {rows, columns}, r);
      }
docs: Random normal using the given rng
  
  @param rows    the number of rows in the matrix
  @param columns the number of columns in the matrix
  @param r       the random generator to use
  @return