update d3, Plot, stdlib (#370)

* update d3, Plot, stdlib

* yarn upgrade @observablehq/stdlib

upgrade stdlib, @observablehq/plot 0.6.13 (#369)

@observablehq/plot 0.6.12 (#368)

5.9.5: upgrade stdlib to 5.8.4 (#367)

5.9.4 (#366)

@observablehq/plot 0.6.11 (#364)

* @observablehq/plot 0.6.11

* @observablehq/runtime 5.9.3

5.9.2 (#363)

* 5.9.2

* better dual-audience contributing guidelines

* mention rollup

5.9.1 (#361)

5.9.0 (#359)

* @observablehq/stdlib 5.8.0

* 5.9.0

@observablehq/plot 0.6.9 (#357)

* @observablehq/plot 0.6.9

* 5.8.2