Make test suite pass on OTP-22

- fix some bad typespec
- bump the meck version for good fortune

rebar.config

@@ -45,7 +45,7 @@
 
 %% Profiles
 {profiles, [{test, [
-                   {deps, [{meck, "0.8.12"}]},
+                   {deps, [{meck, "0.8.13"}]},
                    {erl_opts, [debug_info, nowarn_export_all]}
                    ]
             },

src/rebar_utils.erl

@@ -972,7 +972,7 @@ get_proxy_auth() ->
         {ok, ProxyAuth} -> ProxyAuth
     end.
 
--spec rebar_utils:is_list_of_strings(term()) -> boolean().
+-spec is_list_of_strings(term()) -> boolean().
 is_list_of_strings(List) when not is_list(hd(List)) ->
     false;
 is_list_of_strings(List) when is_list(hd(List)) ->