set qrcode window background to white

shadowsocks-csharp/View/QRCodeForm.Designer.cs

@@ -60,6 +60,7 @@
             // 
             this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
             this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
+            this.BackColor = System.Drawing.Color.White;
             this.ClientSize = new System.Drawing.Size(224, 222);
             this.Controls.Add(this.panel1);
             this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;