update version on install instructions to 0.20.0

[fiatjaf]

fixes #402

[sjrd]

I could merge this, but it would be overwritten by a bot on the next merge on main. The actual source for this is at

scalajs-bundler/manual/src/ornate/index.md

Lines 11 to 14 in b370241

	// For Scala.js 1.x
	addSbtPlugin("ch.epfl.scala" % "sbt-scalajs-bundler" % "{{version}}")
	// Or, for Scala.js 0.6.x
	addSbtPlugin("ch.epfl.scala" % "sbt-scalajs-bundler-sjs06" % "{{version}}")

We should probably replace the dynamic {{version}}s by hard-corded ones.

[fiatjaf]

Why is the {{version}} printing the wrong value though? It would work if {{version}} corresponded to the latest release.

[sjrd]

I don't know. It's possible that the value of {{version}} comes from

scalajs-bundler/manual/src/ornate.conf

Line 17 in d083e6d

version = ${version}

However, I don't know where the ${version} comes from. 🤷‍♂️

[fiatjaf]

ahahah, well, apparently it is a built-in thing from ornate, and there seems to be also a ${tag} value.

I should try to rebuild the pages using that and send a proper PR, but I'm just trying to learn the basic of basics of Scala here and all these sbt things are imploding my head already so I'll refrain from doing it now :P