Fix for Dictionary changed from object to trait

This fixes the compilation problem. However test still has an error 
triplerush-evaluation\src\test\scala\com\signalcollect\triplerush\TopKSpec.scala:27: not found: type TestAnnouncements
[error] class TopKSpec extends FlatSpec with Matchers with TestAnnouncements {
[error]                                                    ^
[error] one error found
[error] (triplerush-evaluation/test:compile) Compilation failed