Patch for when we pass a nil argument to make

* This bug occurs when we do not have ENV['MAKEFLAGS'] available, such
as when we are building from Sublime Text (nomdev.sublime-build).

For the time being, passing nomdev.rb build --threads [# of jobs]
within nomdev.sublime-build script will suffice to limit the number of
jobs make may generate. When not specified, this instructs make to not
limit number of jobs.