change from Numo::Gnuplot::GnuplotError to Numo::GnuplotError. Gnuplot#replot accept argument. avoid string quotation after "log" keyword.
change from Numo::Gnuplot::GnuplotError to Numo::GnuplotError.
Gnuplot#replot accept argument.
avoid string quotation after "log" keyword.

ruby-numo/gnuplot