The solution to this problem is mentioned in [the Intl docs](http://symfony.com/doc/current/components/intl.html):

> A better solution is to fix your composer.json to the version required by the production server. First, determine the ICU version on the server:
>
>```
> $ php -i | grep ICU
> ICU version => 4.2.1
> ```
>
>Then fix the ICU component in your composer.json file to a matching version:
>
> ```json
> "require: {
>     "symfony/icu": "1.1.*"
> }