Update dependency composer/installers to v1.12.0

This MR contains the following updates:

Package	Type	Update	Change
composer/installers (source)	require	minor	1.11.0 -> 1.12.0

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Release Notes

composer/installers

v1.12.0

Compare Source

Added

• Added installer for Pantheon Quicksilver modules/scripts #​495.

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docker/build.sh

@@ -18,10 +18,13 @@ PACKAGES="
         libapache2-mod-xsendfile
         libapache2-mod-security2
         modsecurity-crs
-        php-xml
+        php-imagick
+        php-intl
         php-mysql
         php-memcached
         php-mbstring
+        php-xml
+        php-zip
 
         noblogs-cli
 "