Fix doc

Author: mohanson

doc/zh/markdown/content/project_mainnet.md

@@ -54,7 +54,7 @@ pxsol.config.current = pxsol.config.mainnet # Mainnet Beta
 import pxsol
 
 pxsol.config.current = pxsol.config.mainnet
-pxsol.config.current.rpc.cooldown = 1
+pxsol.config.current.rpc.qps = 1
 pxsol.config.current.rpc.url = 'https://api.mainnet-beta.solana.com'
 ```