Fix example code in ReadMe

[popod]

Your example code does not works in my Mac (High Sierra and node v8.6.0):

var Opened = require('@ronomon/opened');
var paths = ['./test.txt'];
Opened.files(paths,
  function(error, hashTable) {
    if (error) throw error;
    paths.forEach(
      function(path) {
        console.log(path + ' open=' + hashTable.hasOwnProperty(path));
      }
    );
  }
);

hashTable contain { 'test.txt': true|false } so you should use:

console.log(path + ' open=' + hashTable[path]);

In place of:

console.log(path + ' open=' + hashTable.hasOwnProperty(path));

---

I've too:

• add an API section to the README to explain what is returned from .file() or .files().
• fix a bug with .file() on Unix systems

[jorangreef]

Thanks @popod, I did another PR quickly with all your fixes but I didn't want to expose Open.file() in the docs just yet.

Thanks for spotting this, I don't know how I missed it.