lazy val root = (project in file(".")).enablePlugins(SbtWeb)

lazy val playVersion = settingKey[String]("Play version in relation to current Scala Version")

playVersion := {
  CrossVersion.partialVersion(scalaVersion.value) match {
    case Some((2, 10)) => "2.4.0-2"
    case Some((2, n)) if n > 10 => "2.6.2"
  }
}

libraryDependencies ++= Seq(
  "org.webjars.bower" % "bootstrap-sass" % "3.3.6",
  "org.webjars" %% "webjars-play" % playVersion.value
)

lazy val root = (project in file(".")).enablePlugins(SbtWeb)

libraryDependencies ++= Seq(
  "org.webjars.bower" % "bootstrap-sass" % "3.3.6",
  "org.webjars" %% "webjars-play" % "2.6.2"
)

--- 
+++ 
@@ -1,6 +1,15 @@
 lazy val root = (project in file(".")).enablePlugins(SbtWeb)
+
+lazy val playVersion = settingKey[String]("Play version in relation to current Scala Version")
+
+playVersion := {
+  CrossVersion.partialVersion(scalaVersion.value) match {
+    case Some((2, 10)) => "2.4.0-2"
+    case Some((2, n)) if n > 10 => "2.6.2"
+  }
+}
 
 libraryDependencies ++= Seq(
   "org.webjars.bower" % "bootstrap-sass" % "3.3.6",
-  "org.webjars" %% "webjars-play" % "2.6.2"
+  "org.webjars" %% "webjars-play" % playVersion.value
 )
Determine Play's version depending on Scala Version
