Fix: broken prepare statement in MySqlAdapter for MySql > 5.7

MySql introduced a sql mode called only_full_group_by which broke
the prepare statement method. This is a workaround to be backwards
compatible.

src/Adapter/MySQLAdapter.php

@@ -246,7 +246,10 @@ public function prepareStatement($query, $options, $limit, $offset)
             $objectsTable,
             $objectsTable
         );
-
+        // fix for the mysqli >= 5.7 only_full_group_by bug
+        if($this->connection->server_version >= 50700) {
+            $this->connection->query("SET SESSION sql_mode=''");
+        }
         $query = sprintf(
             'SELECT %s
             FROM %s as  rootContents