use slash style consistently in build definition

Author: SethTisue

build.sbt

@@ -6,15 +6,15 @@ lazy val swing = project.in(file("."))
     OsgiKeys.exportPackage := Seq(s"scala.swing.*;version=${version.value}"),
     scalaModuleMimaPreviousVersion := Some("2.1.0"),
     // set the prompt (for this build) to include the project id.
-    shellPrompt in ThisBuild := { state => Project.extract(state).currentRef.project + "> " },
+    ThisBuild / shellPrompt := { state => Project.extract(state).currentRef.project + "> " },
     libraryDependencies ++= Seq(
       "org.scalatest" %% "scalatest-flatspec" % "3.2.0" % Test,
       "org.scalatest" %% "scalatest-shouldmatchers" % "3.2.0" % Test,
     ),
     // Adds a `src/main/scala-2.13+` source directory for Scala 2.13 and newer
     // and  a `src/main/scala-2.13-` source directory for Scala version older than 2.13
-    unmanagedSourceDirectories in Compile += {
-      val sourceDir = (sourceDirectory in Compile).value
+    Compile / unmanagedSourceDirectories += {
+      val sourceDir = (Compile / sourceDirectory).value
       CrossVersion.partialVersion(scalaVersion.value) match {
         case Some((2, n)) if n >= 13 => sourceDir / "scala-2.13+"
         case _                       => sourceDir / "scala-2.13-"
@@ -25,15 +25,15 @@ lazy val swing = project.in(file("."))
 lazy val examples = project.in(file("examples"))
   .dependsOn(swing)
   .settings(
-    scalaVersion := (scalaVersion in swing).value,
-    fork in run := true,
+    scalaVersion := (swing / scalaVersion).value,
+    run / fork := true,
     fork := true
   )
 
 lazy val uitest = project.in(file("uitest"))
   .dependsOn(swing)
   .settings(
-    scalaVersion := (scalaVersion in swing).value,
-    fork in run := true,
+    scalaVersion := (swing / scalaVersion).value,
+    run / fork := true,
     fork := true
   )