README: updated the minimum version of ngx_lua and ngx_openresty that we require.

Author: agentzh

README.markdown

@@ -26,7 +26,7 @@ This is how streaming reading works. Even for giga bytes of file data input, the
 This Lua library takes advantage of ngx_lua's cosocket API, which ensures
 100% nonblocking behavior.
 
-Note that at least [ngx_lua 0.5.0rc5](https://github.com/chaoslawful/lua-nginx-module/tags) or [ngx_openresty 1.0.11.7](http://openresty.org/#Download) is required.
+Note that at least [ngx_lua 0.5.0rc25](https://github.com/chaoslawful/lua-nginx-module/tags) or [ngx_openresty 1.0.15.1](http://openresty.org/#Download) is required.
 
 Synopsis
 ========