Fixed constructor of Aggregator to make __repr__ of Collector possible
Fixed constructor of Aggregator to make __repr__ of Collector possible

ioam/holoviews,mjabri/holoviews,basnijholt/holoviews,vascotenner/holoviews,mjabri/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews,mjabri/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews