Add ArrayBuilder to whitelist

Author: odersky

test/dotc/scala-collections.whitelist

@@ -86,6 +86,8 @@
 #./scala-scala/src/library/scala/collection/mutable/IndexedSeq.scala
 #./scala-scala/src/library/scala/collection/mutable/ListBuffer.scala
 
+./scala-scala/src/library/scala/collection/mutable/ArrayBuilder.scala
+
 ./scala-scala/src/library/scala/collection/immutable/Stack.scala
 ./scala-scala/src/library/scala/collection/immutable/StringLike.scala
 ./scala-scala/src/library/scala/collection/immutable/StringOps.scala
@@ -203,7 +205,7 @@
 
 
 ./scala-scala/src/library/scala/collection/immutable/HashMap.scala
-
+x
 # seems https://github.com/lampepfl/dotty/issues/916
 #./scala-scala/src/library/scala/collection/immutable/HashSet.scala