Made scala 2.12 default

Author: bhermann

build.sbt

@@ -24,9 +24,9 @@ ThisBuild / homepage := Some(url("https://delphi.cs.uni-paderborn.de/"))
 
 lazy val scala212 = "2.12.10"
 lazy val scala213 = "2.13.1"
-lazy val supportedScalaVersions = List(scala212, scala213)
+lazy val supportedScalaVersions = List(scala212)
 
-ThisBuild / scalaVersion := scala213
+ThisBuild / scalaVersion := scala212
 
 name := "delphi"
 version := "1.0.0-SNAPSHOT"