Simplify 'buffer' signature to be the same as 'window'.
Simplify 'buffer' signature to be the same as 'window'.

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