fix --watch not finding any files to execute; closes #3748

[boneskull]

...missing parameter.

[boneskull]

appveyor is killing me today

[plroebuck]

BTW...

$ DEBUG=* /var/tmp/mocha-ya/bin/_mocha --require coffee-script/register --extension="coffee"
  mocha:cli:cli entered main with raw args [ '--require',
  'coffee-script/register',
  '--extension=coffee' ] +0ms
  mocha:cli:options no config found in /var/tmp/sample-node-typescript-module/package.json +0ms
  mocha:cli:options No mocha.opts found at ./test/mocha.opts +48ms
  mocha:cli:run:helpers loaded require "coffee-script/register" +0ms
  mocha:cli:run post-yargs config { _: [],
  diff: true,
  require: [ 'coffee-script/register' ],
  r: [ 'coffee-script/register' ],
  extension: [ 'coffee', 'js' ],
  'watch-extensions': [ 'coffee', 'js' ],       // <= :NOTE: camelCase version is different...
  watchExtensions: [ 'coffee' ],
  opts: false,
  reporter: 'spec',
  R: 'spec',
  slow: 75,
  s: 75,
  timeout: 2000,
  t: 2000,
  timeouts: 2000,
  ui: 'bdd',
  u: 'bdd',
  spec: [ 'test/' ],
  config: false,
  package: false,
  '$0': 'mocha' } +0ms
...

[boneskull]

camelcase args are thrown out at some point in there before we get to _mocha