The "string" option type doesn't accept '-' as a value

[fardog]

For example:

var opts = require('nomnom')
  .option('separator', {
    abbr: 's',
    default: ' ',
    type: "string",
    help: 'The separator character to use between words when output to the console.'
  })
  .parse();

then calling the application with:

./app -s '-'

will result in:

'-separator' expects a value

I've tried other combinations of this, such as:

./app -s \-
./app --separator \-
./app --separator '-'
./app --separator "-"

All to no avail. Seem that a dash won't be accepted as a string.