fix: normalized keys were not enumerable

[bcoe]

This was breaking upstream behavior in yargs (and in turn mocha), because the parsed options object is iterated over in yargs and appended to another object:

mocha init <path>

create a client-side Mocha setup at <path>

Positional Arguments
  path                                                       [string] [required]

Other Options
  --help, -h     Show usage information & exit                         [boolean]
  --version, -V  Show version number & exit                            [boolean]

✖ ERROR: Missing required argument: path