update donation

@@ -9,7 +9,8 @@ Download from github.io: [Centos6-x86_64][centos0], [more...][more0]<br/>
 Download from ossrs.net: [Centos6-x86_64][centos1], [more...][more1]<br/>
 Website for SRS/2.0, read SRS 2.0 [Chinese][srs2_CN] or [English][srs2_EN].
 
-[![Donation](https://www.paypal.com/en_US/i/btn/btn_donate_LG.gif)](http://www.ossrs.net/srs.release/donation/index.html)
+[![Donation](https://www.paypalobjects.com/webstatic/en_US/btn/btn_donate_92x26.png)](http://www.ossrs.net/srs.release/donation/index.html)
+[![Paypal](https://www.paypalobjects.com/webstatic/en_US/btn/btn_donate_pp_142x27.png)](http://www.ossrs.net/srs.release/donation/paypal.html)
 
 ## Why SRS?