DOC: lua: update the links to the config and Lua API

The links were still stuck to version 1.6. Let's update them.

The patch needs to be carefully backported to 1.8 and 1.7 after
editing the respective version (replace 1.9dev with 1.8 or 1.7).
diff --git a/doc/lua.txt b/doc/lua.txt
index 7dded13..4a5ea43 100644
--- a/doc/lua.txt
+++ b/doc/lua.txt
@@ -83,9 +83,9 @@
 Reading the following documentation links is required to understand the
 current paragraph:
 
-   HAProxy doc: http://cbonte.github.io/haproxy-dconv/configuration-1.6.html
+   HAProxy doc: http://cbonte.github.io/haproxy-dconv/
    Lua API:     http://www.lua.org/manual/5.3/
-   HAProxy API: http://www.arpalert.org/src/haproxy-lua-api/1.6/index.html
+   HAProxy API: http://www.arpalert.org/src/haproxy-lua-api/1.9dev/index.html
    Lua guide:   http://www.lua.org/pil/
 
 more about Lua choice