Bug in auto/autoInject for tasks of the form `[ <function> ]`

[miguel76]

In .auto(), tasks with no dependencies may be defined either by a function or an array containing a single function.
The second form actually gives an error cause in this line the array get enclosed in another array.
This is not crucial .auto() itself, but a bit limiting when using .autoInject(), cause the array form is an alternative to using explicit parameters, like in the example below.

async.autoInject({
  'input-string': [async.apply(fs.readFile, inputFilename, 'utf8')],
  input: ['input-string', async.asyncify(JSON.parse)],
  ...
}, callback);