Fix logic for isReplicaSet

This function was introduced in 7a54cbe and only used in one test.

Author: jmikola

tests/Database/DatabaseFunctionalTest.php

@@ -102,7 +102,7 @@ public function testCommand()
 
     public function testCommandDoesNotInheritReadPreference()
     {
-        if ($this->isReplicaSet()) {
+        if (! $this->isReplicaSet()) {
             $this->markTestSkipped('Test only applies to replica sets');
         }
 

tests/FunctionalTestCase.php

@@ -303,7 +303,7 @@ protected function getServerStorageEngine(ReadPreference $readPreference = null)
 
     protected function isReplicaSet()
     {
-        return $this->getPrimaryServer()->getType() !== Server::TYPE_RS_PRIMARY;
+        return $this->getPrimaryServer()->getType() == Server::TYPE_RS_PRIMARY;
     }
 
     protected function isShardedCluster()