Update cats-core to 2.3.1

Author: 47erbot

build.sbt

@@ -18,7 +18,7 @@ lazy val exercises = (project in file("."))
     libraryDependencies ++= Seq(
       "org.scala-exercises"        %% "exercise-compiler"         % "0.6.7",
       "org.scala-exercises"        %% "definitions"               % "0.6.7",
-      "org.typelevel"              %% "cats-core"                 % "2.2.0",
+      "org.typelevel"              %% "cats-core"                 % "2.3.1",
       "com.chuusai"                %% "shapeless"                 % "2.3.3",
       "org.scalatest"              %% "scalatest"                 % "3.2.3",
       "org.scalacheck"             %% "scalacheck"                % "1.15.2",