Fix capitalisation of "Lua" in the readme (radareorg#7489)

According to the Lua website,[1] only the first letter of "Lua"
should be capitalized, so do the same here in README.md.

[1] https://www.lua.org/about.html

README.md

@@ -99,7 +99,7 @@ To update package use the command
 
 All language bindings are under the r2-bindings directory.
 You will need to install swig and valabind in order to
-build the bindings for Python, LUA, etc..
+build the bindings for Python, Lua, etc..
 
 APIs are defined in vapi files which are then translated
 to swig interfaces, nodejs-ffi or other and then compiled.