Multiple 404s on old Skills Matter events

[SethTisue]

For the Links > External check, the following failures were found:
* At ./_site/pastevents/index.html:975:
  External link https://skillsmatter.com/event/scala/scala-exchange-2013 failed (status code 404)
* At ./_site/pastevents/index.html:1120:
  External link https://skillsmatter.com/event/scala/functional-programming-exchange-1819/mh-8499 failed (status code 404)
* At ./_site/pastevents/index.html:1533:
  External link https://skillsmatter.com/event/scala/scala-exchange-2014 failed (status code 404)
* At ./_site/pastevents/index.html:2099:
  External link https://skillsmatter.com/conferences/6862-scala-exchange-2015 failed (status code 404)
* At ./_site/pastevents/index.html:2863:
  External link https://skillsmatter.com/conferences/7432-scala-exchange-2016 failed (status code 404)
* At ./_site/pastevents/index.html:3638:
  External link https://skillsmatter.com/conferences/8784-scala-exchange-2017 failed (status code 404)
* At ./_site/pastevents/index.html:4394:
  External link https://skillsmatter.com/conferences/10488-scala-exchange-2018 failed (status code 404)

volunteer to find a suitable solution? sometimes we can find a YouTube channel to link to instead, or a more top-level page even if it doesn't have information about that specific year