Update twig/twig requirement from ^2.11 to ^2.12

[dependabot-preview]

Updates the requirements on twig/twig to permit the latest version.

Changelog

Sourced from twig/twig's changelog.

• 2.12.0 (2019-10-05)

• added the spaceship operator ("<=>"), useful when using an arrow function in the "sort" filter

• added support for an "arrow" function on the "sort" filter

• added the CssInliner extension in the "extra" repositories: "inline_css"
  filter

• added the Inky extension in the "extra" repositories: "inky_to_html" filter

• added Intl extension in the "extra" repositories: "country_name",
  "currency_name", "currency_symbol", "language_name", "locale_name",
  "timezone_name", "format_currency", "format_number",
  "format_*_number", "format_datetime", "format_date", and "format_time"
  filters, and the "country_timezones" function

• added the Markdown extension in the "extra" repositories: "markdown_to_html",
  and "html_to_markdown" filters

• added the HtmlExtension extension in the "extra" repositories: "date_uri"
  filter, and "html_classes" function

• optimized "block('foo') ?? 'bar'"

• fixed the empty test on Traversable instances

• fixed array_key_exists() on objects

• fixed cache when opcache is installed but disabled

• fixed using macros in arrow functions

• fixed split filter on edge case

• 2.11.3 (2019-06-18)

• display partial output (PHP buffer) when an error occurs in debug mode

• fixed the filter filter (allow the result to be used several times)

• fixed macro auto-import when a template contains only macros

• 2.11.2 (2019-06-05)

• fixed macro auto-import

• 2.11.1 (2019-06-04)

• added support for "Twig\Markup" instances in the "in" test (again)

• allowed string operators as variables names in assignments

• fixed support for macros defined in parent templates

• 2.11.0 (2019-05-31)

• added the possibility to register classes/interfaces as being safe for the escaper ("EscaperExtension::addSafeClass()")

• deprecated CoreExtension::setEscaper() and CoreExtension::getEscapers() in favor of the same methods on EscaperExtension

• macros are now auto-imported in the template they are defined (under the _self variable)

• added support for macros on "is defined" tests

• fixed macros "import" when using the same name in the parent and child templates

• fixed recursive macros

• macros imported "globally" in a template are now available in macros without re-importing them

• fixed the "filter" filter when the argument is \Traversable but does not implement \Iterator (\SimpleXmlElement for instance)

• fixed a PHP fatal error when calling a macro imported in a block in a nested block

... (truncated)

Commits

• c7a85fd Prepare the 2.12.0 release
• 231a365 Update CHANGELOG
• 4625774 feature #3157 Twig 2 is compatible with PHP 7.0 (nicolas-grekas)
• f8c5f86 Merge branch '1.x' into 2.x
• 8909a16 minor #3163 Fix issue #3159 (ericmorand)
• cfac11e Fix issue #3159
• 0d2b2aa minor #3164 Fix issue #3160 (ericmorand)
• 4eb40f2 Fix issue #3160
• b845ed9 Twig 2 is compatible with PHP 7.0
• c2fd999 Merge branch '1.x' into 2.x
• Additional commits viewable in compare view

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