luaPackages: rename std._debug to std__debug

Similarly rename std.normalize to std_normalize.
Having a dot in the name prevents some changes to the lua infrastructure,
for instance passing attribute names { std._debug }: to a function would fail with
`syntax error, unexpected ',', expecting '.' or '=',`

maintainers/scripts/luarocks-packages.csv

@@ -22,6 +22,8 @@ luaffi,,http://luarocks.org/dev,
 luuid,
 penlight,
 say,
+std__debug,std._debug,
+std_normalize,std.normalize,
 luv,
 luasystem,
 mediator_lua,,http://luarocks.org/manifests/teto