Symfony version(s) affected: >=2.3

Description
According to Symfonys documentation page [1] and to the docopt [2] definition, a short option (Options defined with one -) should be followed immediately by the value, or by an optional space. For example: -fFILE or -f FILE.

In the class Symfony\Component\Console\Input\ArrayInput, the method __toString(), formats an input like ['-f' => 'file'] as -f=file, which is not expected (Expected -f file or -ffile).

How to reproduce

        $args = [
            '-f' => 'file',
            'foo' => 'bar',
        ];

        $input = new ArrayInput($args);
        $this->assertEquals('-f file bar', $input->__toString());

Failed asserting that two strings are equal.
Expected :'-f file bar'
Actual   :'-f=file bar'

Possible Solution
Fix the __toString() method to take into consideration - vs -- when assigning with =. The last commit introduced the issue, as it was previously working as expected. It can be seen in the tests on commit: https://github.com/symfony/symfony/blame/659eb663c69e0ef989ada10b0dd36b1c05c78c2c/src/Symfony/Component/Console/Tests/Input/ArrayInputTest.php

I'm working on a PR.