Allow ext-mongodb 1.1.0

While 1.1.1 is required for PHP 7 support, we technically only depend on the 1.1.0 API (this is more relevant for HHVM).

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": ">=5.4",
-        "ext-mongodb": "^1.1.1"
+        "ext-mongodb": "^1.1.0"
     },
     "autoload": {
         "psr-4": { "MongoDB\\": "src/" },