keep up with latest 2.13 changes

this makes the code compile, but there are still test failures.
it's okay, the 2.13 community build won't let us forget.

Author: SethTisue

build.sbt

@@ -5,7 +5,7 @@ version in ThisBuild := "0.1.3-SNAPSHOT"
 resolvers in ThisBuild += "scala-integration" at "https://scala-ci.typesafe.com/artifactory/scala-integration/"
 
 scalaVersionsByJvm in ThisBuild := {
-  val v213 = "2.13.0-pre-e959f6c"  // Feb 5
+  val v213 = "2.13.0-pre-d645559"  // Feb 27
   Map(
     8 -> List(v213 -> true),
     11 -> List(v213 -> false))

core/src/main/scala/scala/collection/parallel/mutable/ParHashMap.scala

@@ -62,7 +62,7 @@ self =>
 
   def splitter = new ParHashMapIterator(1, table.length, size, table(0).asInstanceOf[DefaultEntry[K, V]])
 
-  def knownSize = tableSize
+  override def knownSize = tableSize
 
   def clear() = clearTable()
 

core/src/main/scala/scala/collection/parallel/mutable/ParHashSet.scala

@@ -63,7 +63,7 @@ extends ParSet[T]
   // TODO Redesign ParHashSet so that it can be converted to a mutable.HashSet in constant time
   def seq = scala.collection.mutable.HashSet.from(this)
 
-  def knownSize = tableSize
+  override def knownSize = tableSize
 
   def addOne(elem: T) = {
     addElem(elem)

core/src/main/scala/scala/collection/parallel/mutable/ParMap.scala

@@ -71,7 +71,7 @@ object ParMap extends ParMapFactory[ParMap] {
 
   class WithDefault[K, V](underlying: ParMap[K, V], d: K => V)
   extends scala.collection.parallel.ParMap.WithDefault(underlying, d) with ParMap[K, V] {
-    def knownSize = underlying.knownSize
+    override def knownSize = underlying.knownSize
     def addOne(kv: (K, V)) = {underlying += kv; this}
     def subtractOne(key: K) = {underlying -= key; this}
     override def empty = new WithDefault(underlying.empty, d)

core/src/main/scala/scala/collection/parallel/mutable/ParTrieMap.scala

@@ -90,7 +90,7 @@ extends ParMap[K, V]
     }
   }
 
-  def knownSize = -1
+  override def knownSize = -1
 
   override def stringPrefix = "ParTrieMap"