Add replacement character for space

Hello,

When you minify your css with cssmin for example you obtain this url: `https://fonts.googleapis.com/css?family=OpenSans%3A400%2C600`

cssmin output:
```css
@import url(https://fonts.googleapis.com/css?family=OpenSans%3A400%2C600);
```

but the real url is: `https://fonts.googleapis.com/css?family=Open%20Sans%3A400%2C600`
cssmin output:
```css
@import url(https://fonts.googleapis.com/css?family=Open%20Sans%3A400%2C600);
```

Thanks