Fixing issue with empty directories in composer.json

[moufmouf]

Fixing issue with empty directories in composer.json like:

{
  "autoload" : {
    "psr-4" : {
      "Foo" : ""
    }
}

[coveralls]

Coverage remained the same at 72.414% when pulling 40d35ad on moufmouf:fixing_empty_dir into 2b11a7c on thecodingmachine:1.0.

[coveralls]

Coverage decreased (-0.2%) to 72.254% when pulling 60c0fc7 on moufmouf:fixing_empty_dir into 2b11a7c on thecodingmachine:1.0.