fixing timerThread to count in milliseconds

src/minefield.cpp

@@ -21,7 +21,7 @@ void MineField::timerTick() {
     auto now = std::chrono::system_clock::now();
     const auto duration = now - start;
     std::chrono::milliseconds ms = std::chrono::duration_cast<std::chrono::milliseconds>(duration); 
-    m_time += duration.count();
+    m_time += ms.count();
     timerSignal.emit(m_time);
     start = std::chrono::system_clock::now();
   }