Deal with imagemagick.convert.path on windows

[sbj42]

When I installed ImageMagick on Windows, the name of the program installed is "magick.exe". "convert" is some kind of windows filesystem utility. The imagemagick node module accommodates this by allowing you to set imagemagick.convert.path to work around that. I was able to get cordova-icon to run by hacking
ig.convert.path = "magick" into index.js.

I recommend one of the following:

• Add an option to specify the convert path on the command line (something like if (argv.convertpath) ig.convert.path = argv.convertpath;)

• Switch from the "imagemagick" module to one that deals more gracefully with this OS difference. The current github readme for that module says "This is an abandoned version.", and references another module which in turn says "This code has been unmaintained for a long time. Please consider using the gm module instead." So perhaps "gm" would better handle the windows case?