Links to Dotty documentation changed

[Philippus]

- ./_site/sips/minutes/2018-09-24-sip-minutes.html
  *  External link https://dotty.epfl.ch/docs/reference/dependent-function-types.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/implicit-function-types.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/intersection-types.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/union-types.html failed: 404 No error
- ./_site/sips/minutes/2018-11-26-sip-minutes.html
  *  External link http://dotty.epfl.ch/docs/reference/dependent-function-types.html failed: 404 No error
  *  External link http://dotty.epfl.ch/docs/reference/implicit-function-types.html failed: 404 No error
  *  External link http://dotty.epfl.ch/docs/reference/intersection-types.html failed: 404 No error
  *  External link http://dotty.epfl.ch/docs/reference/union-types.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/changed/implicit-resolution.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/changed/pattern-matching.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/changed/type-checking.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/changed/type-inference.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/dropped/class-shadowing.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/dropped/early-initializers.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/dropped/existential-types.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/dropped/type-projection.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/dropped/weak-conformance.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/trait-parameters.html failed: 404 No error
  *  External link https://dotty.epfl.ch/docs/reference/type-lambdas.html failed: 404 No error
htmlproofer 3.9.1 | Error:  HTML-Proofer found 19 failures!

The url's changed in scala/scala3#5654. Should be easy to update them.