Add setting to have sbt not exit

if a program calls System.exit
Without this a useless and misleading log4j error is reported.

build.sbt

@@ -1,8 +1,8 @@
 // See LICENSE for license details.
 
 val defaultVersions = Map(
-  "chisel3" -> "3.4.+",
-  "chisel-iotesters" -> "1.5.+"
+  "chisel3" -> "3.5-SNAPSHOT",
+  "chisel-iotesters" -> "2.5-SNAPSHOT"
 )
 
 lazy val commonSettings = Seq(
@@ -16,6 +16,8 @@ lazy val commonSettings = Seq(
   libraryDependencies ++= Seq(
     "com.typesafe.play" %% "play-json" % "2.9.2",
     "org.scalatest" %% "scalatest" % "3.2.9" % "test",
+    "org.apache.logging.log4j" % "log4j-api" % "2.11.2",
+    "org.apache.logging.log4j" % "log4j-core" % "2.11.2"
   ),
   resolvers ++= Seq(
     Resolver.sonatypeRepo("snapshots"),
@@ -31,6 +33,7 @@ lazy val commonSettings = Seq(
 lazy val tapeout = (project in file("tapeout"))
   .settings(commonSettings)
   .settings(scalacOptions in Test ++= Seq("-language:reflectiveCalls"))
+  .settings(fork := true)
   .settings(
     mainClass := Some("barstools.macros.MacroCompiler")
   )