Composer: request PHP extention mongodb

[romiafrizal]

Build Fail when installing mongodb:

Your requirements could not be resolved to an installable set of packages.
  Problem 1
    - Installation request for mongodb/mongodb 1.7.1 -> satisfiable by mongodb/mongodb[1.7.1].
    - mongodb/mongodb 1.7.1 requires ext-mongodb ^1.8 -> the requested PHP extension mongodb is missing from your system.
  Problem 2
    - mongodb/mongodb 1.7.1 requires ext-mongodb ^1.8 -> the requested PHP extension mongodb is missing from your system.
    - jenssegers/mongodb v3.6.5 requires mongodb/mongodb ^1.4 -> satisfiable by mongodb/mongodb[1.7.1].
    - Installation request for jenssegers/mongodb v3.6.5 -> satisfiable by jenssegers/mongodb[v3.6.5].

  To enable extensions, verify that they are enabled in your .ini files:
    - /usr/local/etc/php/php-cli.ini
    - /usr/local/etc/php/conf.d/docker-php-ext-sodium.ini
    - /usr/local/etc/php/conf.d/docker-php-ext-zip.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

Affected builder image

gcr.io/cloud-builders-community/composer

Expected Behavior

Composer build step success

Actual Behavior

Composer build step fail

Steps to Reproduce the Problem

1. compser.json

{
    "name": "laravel/lumen",
    "description": "The Laravel Lumen Framework.",
    "keywords": ["framework", "laravel", "lumen"],
    "license": "MIT",
    "type": "project",
    "require": {
. . .
   "mongodb/mongodb": "^1.7",
. . .
},
    "config": {
        "preferred-install": "dist",
        "sort-packages": true,
        "optimize-autoloader": true
    },
    "minimum-stability": "dev",
    "prefer-stable": true
}

Additional Info