Increase maximum heap size for Tycho test
Increase maximum heap size for Tycho test

Without this change expression evaluator tests crash with an OOM on
Eclipse Oxygen.
scala-ide/scala-ide,wpopielarski/scala-ide,wpopielarski/scala-ide,scala-ide/scala-ide,wpopielarski/scala-ide,scala-ide/scala-ide,wpopielarski/scala-ide,scala-ide/scala-ide