mktmp: fix off by one

Reported in:

#41

Thanks @tduccuong!

src/procket.app.src

@@ -2,5 +2,11 @@
     [{description, "Low level socket operations"},
      {applications, []},
      {registered, []},
+     {vsn, "0.9.3"},
+
      {licenses, ["BSD-3"]},
-     {vsn, "0.9.2"}]}.
+     {maintainers, ["Michael Santos"]},
+     {links, [
+         {"Github", "https://github.com/msantos/procket"}
+     ]}
+]}.

src/procket_mktmp.erl

@@ -1,4 +1,4 @@
-%% Copyright (c) 2010-2015, Michael Santos <[email protected]>
+%% Copyright (c) 2010-2017, Michael Santos <[email protected]>
 %% All rights reserved.
 %%
 %% Redistribution and use in source and binary forms, with or without
@@ -60,7 +60,7 @@ template(Name, Chars) ->
     template(lists:reverse(Name), [], Chars).
 template([$X|Rest], Acc, Chars) ->
     template(Rest,
-        [lists:nth(rand:uniform(length(Chars)+1), Chars)|Acc],
+        [lists:nth(rand:uniform(length(Chars)), Chars)|Acc],
         Chars);
 template(Name, Rand, _) when length(Rand) >= 6 ->
     lists:reverse(Name) ++ Rand.