Electric.activation_series() now ignores series with less than 2 items in `when_on` instead of crashing.
Electric.activation_series() now ignores series with less than 2 items
in `when_on` instead of crashing.

josemao/nilmtk,HarllanAndrye/nilmtk,AlexRobson/nilmtk,mmottahedi/nilmtk,nilmtk/nilmtk,nilmtk/nilmtk,jaduimstra/nilmtk,pauldeng/nilmtk