Fix detection of rebar3

Looks like sometimes rebar3 report version that can't be split to 3 fields
by '.', we need only first one so don't match the rest

rebar.config.script

@@ -69,7 +69,7 @@ FilterConfig = fun(F, Cfg, [{Path, true, ModFun, Default} | Tail]) ->
 IsRebar3 = case application:get_key(rebar, vsn) of
 	       {ok, VSN} ->
 		   [VSN1 | _] = string:tokens(VSN, "-"),
-		   [Maj, _Min, _Patch] = string:tokens(VSN1, "."),
+		   [Maj|_] = string:tokens(VSN1, "."),
 		   (list_to_integer(Maj) >= 3);
 	       undefined ->
 		   lists:keymember(mix, 1, application:loaded_applications())