[TwitterBridge] Fix issue "Only variables should be assigned by reference"

From the docs: "The new operator returns a reference automatically, so
assigning the result of new by reference is not allowed as of PHP 7.0.0"

plugins/TwitterBridge/daemons/synctwitterfriends.php

@@ -117,7 +117,7 @@ class SyncTwitterFriendsDaemon extends ParallelizingDaemon
 
         // Note: DataObject::getDatabaseConnection() creates
         // a new connection if there isn't one already
-        $conn = &$flink->getDatabaseConnection();
+        $conn = $flink->getDatabaseConnection();
 
         $this->subscribeTwitterFriends($flink);