Twig price extension requires INTL PHP extension

[joeholdcroft]

We should use the Symfony polyfill once this PR is accepted: symfony/symfony#8588

[lsjroberts]

For reference, this is the output from 192.168.201.100 when running composer install:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for message/cog 1.0.x-dev -> satisfiable by message/cog[1.0.x-dev].
    - message/cog 1.0.x-dev requires ext-intl * -> the requested PHP extension intl is missing from your system.
  Problem 2
    - Installation request for message/cog dev-master -> satisfiable by message/cog[dev-master].
    - message/cog dev-master requires ext-intl * -> the requested PHP extension intl is missing from your system.
  Problem 3
    - Installation request for symfony/icu 1.2.x-dev -> satisfiable by symfony/icu[1.2.x-dev].
    - symfony/icu 1.2.x-dev requires lib-icu >=4.4 -> the requested linked library icu has the wrong version installed or is missing from your system, make sure to have the extension providing it.
  Problem 4
    - symfony/icu 1.2.x-dev requires lib-icu >=4.4 -> the requested linked library icu has the wrong version installed or is missing from your system, make sure to have the extension providing it.
    - symfony/intl dev-master requires symfony/icu ~1.0
-RC -> satisfiable by symfony/icu[1.2.x-dev].
    - Installation request for symfony/intl dev-master -> satisfiable by symfony/intl[dev-master].