My supervisor crashes when I try to start it from eshell?

I'm very new to OTP, I'm trying to create simple example to understand supervisor behaviour:

Here is simple increment server

-module( inc_serv ).
-behaviour( gen_server ).
-export( [ start/0, inc/1, stop/0 ] ).
-export( [ init/1, handle_call/3, terminate/2 ] ).

start() ->
        gen_server:start_link( { local, ?MODULE }, ?MODULE, no_args, [] ).

stop() ->
        gen_server:call( ?MODULE, stop ).

inc( Num ) ->
        gen_server:call( ?MODULE, { num, Num } ).

init( no_args ) ->
        io:format( "~p~n", [ "Increment server started :)" ] ),
        { ok, no_state }.

handle_call( { num, Num }, _From, no_state ) ->
        { reply, Num + 1, no_state };
handle_call( stop, _From, no_state ) ->
        { stop, normal, ok, no_state }.

terminate( Reason, no_state ) ->
        io:format( "~p~n", [ "Increment server stopped" ] ).

And I'd like to make it supervised by this module:

-module( supervisor_inc ).
-behaviour( supervisor ).

-export( [ start/0 ] ).
-export( [ init/1 ] ).

start() ->
        supervisor:start_link( { local, ?MODULE }, ?MODULE, no_args ).

init( no_args ) ->
        process_flag( trap_exit, true ),
        Supervisor_Spec = { one_for_one, 1, 1 },
        IncServ_Spec = {
                inc_serv,
                { inc_serv, start, [] },
                permanent, 2000, worker, [ inc_serv ] },
        { ok, { Supervisor_Spec, [ IncServ_Spec ] } }.

After that I've performed in erlang shell next steps:

1> 
1> c(inc_serv).
{ok,inc_serv}
2> 
2> c(supervisor_inc).
{ok,supervisor_inc}
3> 
3> supervisor_inc:start().
"Increment server started :)"
{ok,<0.43.0>}
4> 
4> inc_serv:inc( 7 ).
8
5> inc_serv:inc( 8 ).
9

After this I've tried next (as I expected I've got error):

6> inc_serv:inc( bad_arg ).
"Increment server stopped"
"Increment server started :)"

=ERROR REPORT=