Set a good default font style

HFUTCourseSimulation/ImageExport.cs

@@ -47,7 +47,7 @@ namespace HFUTCourseSimulation {
             var headerBrush = new SolidBrush(Color.Gray);
             var textBrush = new SolidBrush(Color.Black);
             Brush cellBrush;
-            var textFont = new Font("Arial", 12);
+            var textFont = new Font("Microsoft YaHei UI", 12);
 
             var textMargin = graphics.MeasureString("测试字符", textFont).Height;