Convert array items in the params to a String before shell escaping.

Fixes:
> disk = LinuxAdmin::Disk.local.first.create_partition("primary", disk.size.to_i)
NoMethodError: undefined method `shellescape' for 0:Fixnum
Merge pull request #35 from jrafanie/sanitize_fixnum_params

Convert array items in the params to a String before shell escaping.