Update data science solution

What? Dropping the `it` descriptions is weird here. If you really want more terseness, just make it a single it:

```
it "returns all zeroed data when there are no conversions" do
  expect(subject.conversion_rate).to be_zero
  expect(subject.standard_error).to be_zero
  expect(subject.distribution_range).to eq([0, 0])
end