fix broken links for API reflect docs

[bishabosha]

some guides reference the scala reflect API by the following links:

- https://www.scala-lang.org/api/current/scala-reflect/scala/reflect/api/Names$NameApi.html
- https://www.scala-lang.org/api/current/scala-reflect/scala/reflect/api/StandardNames.html
- etc.

which is failing the html proofer check in CI, these now need to be

- https://www.scala-lang.org/api/2.x/scala-reflect/scala/reflect/api/Names$NameApi.html
- https://www.scala-lang.org/api/2.x/scala-reflect/scala/reflect/api/StandardNames.html
- etc.