Adds symfony/yaml specifically to fix the broken phar.

[typhonius]

Was receiving this error with the phar.

PHP Fatal error:  Uncaught Error: Class 'Symfony\Component\Yaml\Yaml' not found in phar:///usr/local/bin/acquiacli/vendor/consolidation/config/src/Loader/YamlConfigLoader.php:23
Stack trace:
#0 phar:///usr/local/bin/acquiacli/src/Cli/Config.php(49): Consolidation\Config\Loader\YamlConfigLoader->load('phar:///usr/loc...')
#1 phar:///usr/local/bin/acquiacli/bin/acquiacli-robo.php(26): AcquiaCli\Cli\Config->__construct('phar:///usr/loc...')
#2 phar:///usr/local/bin/acquiacli/bin/acquiacli(10): require_once('phar:///usr/loc...')
#3 /usr/local/bin/acquiacli(14): require('phar:///usr/loc...')
#4 {main}
  thrown in phar:///usr/local/bin/acquiacli/vendor/consolidation/config/src/Loader/YamlConfigLoader.php on line 23

Fatal error: Uncaught Error: Class 'Symfony\Component\Yaml\Yaml' not found in phar:///usr/local/bin/acquiacli/vendor/consolidation/config/src/Loader/YamlConfigLoader.php:23
Stack trace:
#0 phar:///usr/local/bin/acquiacli/src/Cli/Config.php(49): Consolidation\Config\Loader\YamlConfigLoader->load('phar:///usr/loc...')
#1 phar:///usr/local/bin/acquiacli/bin/acquiacli-robo.php(26): AcquiaCli\Cli\Config->__construct('phar:///usr/loc...')
#2 phar:///usr/local/bin/acquiacli/bin/acquiacli(10): require_once('phar:///usr/loc...')
#3 /usr/local/bin/acquiacli(14): require('phar:///usr/loc...')
#4 {main}
  thrown in phar:///usr/local/bin/acquiacli/vendor/consolidation/config/src/Loader/YamlConfigLoader.php on line 23