Assert\Currency() throws Only the locale "en" is supported.

Using

``` php
    /**
     * @Assert\NotBlank()
     * @Assert\Currency()
     * @ORM\Column(type="float")
     *
     * @var float
     */
    private $price;
```

Throws: Only the locale "en" is supported.

``` php
    /**
     * @Assert\NotBlank()
     * @ORM\Column(type="float")
     *
     * @var float
     */
    private $price;
```

Works perfekt.
