Update Scala versions to 2.12.13 and 2.13.4

Author: sloshy

build.sbt

@@ -1,6 +1,6 @@
 ThisBuild / organization := "com.47deg"
 ThisBuild / scalaVersion := "2.13.2"
-ThisBuild / crossScalaVersions := Seq("2.12.11", "2.13.2")
+ThisBuild / crossScalaVersions := Seq("2.12.13", "2.13.4")
 
 addCommandAlias("ci-test", "scalafmtCheckAll; scalafmtSbtCheck; mdoc; testCovered")
 addCommandAlias("ci-docs", "github; mdoc; headerCreateAll; publishMicrosite")