fix some 404s

Author: SethTisue

contribute/corelibs.md

@@ -20,4 +20,4 @@ There are several options for contributing to Scala's core libraries. You can:
 For significant new functionality or a whole new API to be considered for
 inclusion in the core Scala distribution, you will be asked to submit a SLIP (Scala Library Improvement Process) document.
 
-Please see [instructions for submitting a new SLIP](https://web.archive.org/web/20180116192845/http://docs.scala-lang.org/sips/slip-submission.html) and familiarize yourself with the [SIP/SLIP](http://docs.scala-lang.org/sips/) section of the Scala documentation site. Also please pay particular attention to the [pre-requisites](http://docs.scala-lang.org/sips/slip-submission.html) before submitting a SLIP.
+Please see [instructions for submitting a new SLIP](https://web.archive.org/web/20180116192845/http://docs.scala-lang.org/sips/slip-submission.html) and familiarize yourself with the [SIP/SLIP](http://docs.scala-lang.org/sips/) section of the Scala documentation site. Also please pay particular attention to the pre-requisites in the instructions before submitting a SLIP.