Change name of scala-library jar in tests

For many tests, we need the `scala-library` jar on the classpath, and we
used to search through the classpath for a JAR whose name contained
`scala-library-2.`. This works great if the `scala-library` on the
classpath comes from Ivy. However, if we use the same version of Scala
as sbt, the `scala-library` will not be taken ouf of the Ivy cache but
from sbt's boot directory. In this case, the JAR will simply be named
`scala-library.jar`.

Author: Duhemm

compiler/test/dotty/Jars.scala

@@ -26,7 +26,7 @@ object Jars {
     dottyLib :: dottyCompiler :: dottyInterfaces :: dottyExtras
 
   def scalaLibrary: String = sys.env.get("DOTTY_SCALA_LIBRARY")
-    .getOrElse(findJarFromRuntime("scala-library-2."))
+    .getOrElse(findJarFromRuntime("scala-library"))
 
   /** Gets the scala 2.* library at runtime, note that doing this is unsafe
    *  unless you know that the library will be on the classpath of the running