Adds cross-compile configuration to make it compatible with scala 12

Author: javierpedreira

.github/workflows/build.yml

@@ -45,4 +45,4 @@ jobs:
       - name: Publish library
         env:
           GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
-        run: sbt publish
+        run: sbt "+publish"

build.sbt

@@ -1,11 +1,18 @@
-ThisBuild / scalaVersion     := "2.13.3"
+import sbt.Keys.scalaVersion
+
 ThisBuild / organization     := "com.intenthq"
 ThisBuild / organizationName := "Intent HQ"
 
+lazy val scala212 = "2.12.12"
+lazy val scala213 = "2.13.3"
+lazy val supportedScalaVersions = List(scala213, scala212)
+
 lazy val root = (project in file("."))
   .settings(
     name := "scala-secret",
-    libraryDependencies += Dependencies.weaver
+    libraryDependencies += Dependencies.weaver,
+    scalaVersion := scala213,
+    crossScalaVersions := supportedScalaVersions
   )
 
 testFrameworks += new TestFramework("weaver.framework.TestFramework")