change weight data download url (#1812)

examples/portfolio/README.md

@@ -20,7 +20,7 @@ We use China stock market data for our example.
 1. Prepare CSI300 weight:
 
    ```bash
-   wget http://fintech.msra.cn/stock_data/downloads/csi300_weight.zip
+   wget https://github.com/SunsetWolf/qlib_dataset/releases/download/v0/csi300_weight.zip
    unzip -d ~/.qlib/qlib_data/cn_data csi300_weight.zip
    rm -f csi300_weight.zip
    ```