Fix indentation

Author: LinasBeres

src/IECoreImage/DisplayDriverServer.cpp

@@ -119,7 +119,7 @@ class DisplayDriverServer::Session : public RefCounted
 		DisplayDriverPtr m_displayDriver;
 		DisplayDriverServerHeader m_header;
 		CharVectorDataPtr m_buffer;
-        std::optional<int> m_mergeId;
+        	std::optional<int> m_mergeId;
 };
 
 class DisplayDriverServer::PrivateData : public RefCounted