Change :epswrite to :eps2write.

`epswrite` has been removed from Ghostscript ([item 2.3 here](http://ghostscript.com/doc/current/Issues.htm)). When attempting to output to EPS, RGhost throws an error that the device doesn't exist when outputting with the `:eps` device. This fixes that by replacing `:epswrite` with `:eps2write`, the new device name in Ghostscript.