Fixed scala compilation error.
Fixed scala compilation error.

zhongdj/RxScala,samuelgruetter/RxScala,jbripley/RxScala,ReactiveX/RxScala,samuelgruetter/RxScala,jbripley/RxScala,hermanbanken/RxScala,hermanbanken/RxScala,zjrstar/RxScala,TracyLu/RxScala,joohnnie/RxScala