cat doesn't support '-n' option

[maunier]

Node version (or tell us if you're using electron or some other framework):

v7.9.0

ShellJS version (the most recent version/Github branch you see the bug on):

0.7.8

Operating system:

osx

Description of the bug:

cat method don't support options,

Example ShellJS command to reproduce the error:

i need to cat a file with line number, but now it dosen't support it

[nfischer]

Yeah, we never implemented options on cat(). Pull requests are welcome!

This feature request calls for the -n option I believe.