fix LDAP install for systems without ldap extension (#846)

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "ed199b91b3e5eb0b9d2a1eb00ea11cba",
+    "content-hash": "67746acda4894c88c47e3afffab130e4",
     "packages": [
         {
             "name": "beberlei/DoctrineExtensions",
@@ -8618,59 +8618,6 @@
             ],
             "time": "2018-04-25T15:33:34+00:00"
         },
-        {
-            "name": "zendframework/zend-ldap",
-            "version": "2.10.0",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/zendframework/zend-ldap.git",
-                "reference": "b63c7884a08d3a6bda60ebcf7d6238cf8ad89f49"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/zendframework/zend-ldap/zipball/b63c7884a08d3a6bda60ebcf7d6238cf8ad89f49",
-                "reference": "b63c7884a08d3a6bda60ebcf7d6238cf8ad89f49",
-                "shasum": ""
-            },
-            "require": {
-                "ext-ldap": "*",
-                "php": "^5.6 || ^7.0"
-            },
-            "require-dev": {
-                "php-mock/php-mock-phpunit": "^1.1.2 || ^2.1.1",
-                "phpunit/phpunit": "^5.7.27 || ^6.5.8 || ^7.1.2",
-                "zendframework/zend-coding-standard": "~1.0.0",
-                "zendframework/zend-config": "^2.5",
-                "zendframework/zend-eventmanager": "^2.6.3 || ^3.0.1",
-                "zendframework/zend-stdlib": "^2.7 || ^3.0"
-            },
-            "suggest": {
-                "zendframework/zend-eventmanager": "Zend\\EventManager component"
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "2.10.x-dev",
-                    "dev-develop": "2.11.x-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "Zend\\Ldap\\": "src/"
-                }
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "BSD-3-Clause"
-            ],
-            "description": "Provides support for LDAP operations including but not limited to binding, searching and modifying entries in an LDAP directory",
-            "keywords": [
-                "ZendFramework",
-                "ldap",
-                "zf"
-            ],
-            "time": "2018-07-05T05:05:12+00:00"
-        },
         {
             "name": "zircote/swagger-php",
             "version": "2.0.14",