Check consistency between chapter and links

[jtr13]

This chapter https://jtr13.github.io/d3book/solutions.html#update-enter-and-exit-horizontal-bar-chart has two versions for many of the solutions: in the chapter and standalone files for which links are provided, such as: https://jtr13.github.io/d3book/solutions/general_update_pattern_vertical.html There are discrepancies that need to be fixed. One is that some files have: .attr("y", (d, i) => 50 * i) and others have: .attr("y", (d, i) => 50 * i + 50) (And the same for x for vertical bar charts.) All should be 50 * i.