Update build.sbt

Author: shunjikonishi

build.sbt

@@ -4,9 +4,9 @@ name := """github-api"""
 
 version := "0.3.0-SNAPSHOT"
 
-scalaVersion := "2.12.10"
+scalaVersion := "2.13.1"
 
-crossScalaVersions := Seq("2.10.7", "2.11.12", scalaVersion.value, "2.13.1")
+crossScalaVersions := Seq("2.10.7", "2.11.12", "2.12.10", "2.13.1")
 
 description := "The GitHub API from Scala with Async HTTP Client (Netty)"