Merge branch '29-explore-banner' into 'master'

Resolve "更新 explore 页的 banner 域名"

Closes #29

See merge request codechina/operation-work!109

explore/index.yml

 banner:
-- link: https://codechina.csdn.net/courses/detail/1/l
+- link: /courses/detail/1/l
   url: https://codechina.csdn.net/codechina/operation-work/uploads/3d1c29bc9e4003473c6f746c075722cb/Git%E5%9F%BA%E7%A1%80%E5%85%A5%E9%97%A8.jpg
 groups:
 - csdn
@@ -17,7 +17,7 @@ groups:
 - chatopera
 - opendilab 
 learning_banner:
-- link: https://codechina.csdn.net/courses
+- link: /courses
   url: https://codechina.csdn.net/codechina/operation-work/uploads/38be577289ba8800a9caa233416cd4b6/1920x480_1_.png
 projects:
 - hihell/python120