alcaeus/mongo-php-adapter is not a hard dependency anymore

composer.json

@@ -15,7 +15,6 @@
     },
     "require": {
         "php": ">=5.3.0",
-        "alcaeus/mongo-php-adapter": "^1.0",
         "paragonie/random_compat": ">=2.0"
     },
     "suggest": {
@@ -24,6 +23,7 @@
         "ext-mongo": "Mongo is needed to store profiler results for PHP < 7.",
         "ext-mongodb": "Mongo is needed to store profiler results for PHP > 7.",
         "ext-curl": "You need to install the curl extension to upload saved files",
+        "ext-pdo": "You need to install the pdo extension to store profiler results to a relational database",
         "alcaeus/mongo-php-adapter": "Mongo PHP Adapter is required for PHP >7 (when using ext-mongodb)"
     }
 }