fix scala.reflect.Manifest scaladoc
fix scala.reflect.Manifest scaladoc

- Predef.classManifest no longer exists https://github.com/scala/scala/commit/ed614acf789b2ef5dd0624a90ea5f43714d5da0d#diff-532a778b9b259c18ed28fd43a22e44feL207
- ClassManifest is deprecated. use Manifest
- erasure is deprecated. use runtimeClass

```
Welcome to Scala 2.13.0-M4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_172).
Type in expressions for evaluation. Or try :help.

scala> def methods[T: Manifest] = manifest[T].runtimeClass.getMethods
methods: [T](implicit evidence$1: Manifest[T])Array[java.lang.reflect.Method]

scala> def retType[T: Manifest](name: String) =
     |   methods[T] find (_.getName == name) map (_.getGenericReturnType)
retType: [T](name: String)(implicit evidence$1: Manifest[T])Option[java.lang.reflect.Type]

scala> retType[Map[_, _]]("values")
res0: Option[java.lang.reflect.Type] = Some(scala.collection.Iterable<V>)
```

scala/scala,martijnhoekstra/scala,scala/scala,lrytz/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,scala/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,lrytz/scala,martijnhoekstra/scala,scala/scala