Fixed an issue on locales that use a comma as decimal separator

[jtabet]

If you are using a locale that has a comma as decimal separator, it breaks the url generation. The purpose of this pull request is to fix this issue.
Example:

cloudinary_url('my_pic', ['zoom' => 0.7]);
// Result: http://res.cloudinary.com/xxx/image/upload/z_0,7/my_pic.jpg
// Should be: http://res.cloudinary.com/xxx/image/upload/z_0.7/my_pic.jpg

[tocker]

@jtabet thanks for the pull request!