Undo JVM forking in test, reverting scala#112

* build.sbt (fork): SBT was leaking scala-xml from scala-compiler
because of an incorrect library dependency exclude rule.

Author: ashawley

build.sbt

@@ -29,11 +29,7 @@ lazy val xml = crossProject.in(file("."))
       libraryDependencies += "junit" % "junit" % "4.11" % "test",
       libraryDependencies += "com.novocode" % "junit-interface" % "0.10" % "test",
       libraryDependencies += ("org.scala-lang" % "scala-compiler" % scalaVersion.value % "test").exclude("org.scala-lang.modules", s"scala-xml_${scalaVersion.value}"),
-      mimaPreviousVersion := Some("1.0.5"),
-      // You cannot disable JVM test forking when working on scala modules
-      // that are distributed with the compiler because of an SBT
-      // classloader leaking issue (scala/scala-xml#20 and #112).
-      fork in Test := true): _*)
+      mimaPreviousVersion := Some("1.0.5")): _*)
   .jsConfigure(_.enablePlugins(ScalaJSJUnitPlugin))
 
 lazy val xmlJVM = xml.jvm