minor fix in readme

Author: chronolaw

README.markdown

@@ -269,8 +269,8 @@ in the current request before you reusing the `ctx` table in some other place.
 ## resty.core.socket
 
 * [socket.setoption](https://github.com/openresty/lua-nginx-module#tcpsocksetoption)
-* [socket:setclientcert](https://github.com/openresty/lua-nginx-module#tcpsocksetclientcert)
-* [socket:sslhandshake](https://github.com/openresty/lua-nginx-module#tcpsocksslhandshake)
+* [socket.setclientcert](https://github.com/openresty/lua-nginx-module#tcpsocksetclientcert)
+* [socket.sslhandshake](https://github.com/openresty/lua-nginx-module#tcpsocksslhandshake)
 
 [Back to TOC](#table-of-contents)