PROXY_HEARTBEAT_INTERVAL not parsed as integer

[marcellanz]

Starting massa with:

PROXY_HEARTBEAT_INTERVAL=3000 iex --name massa-001@127.0.0.1 -S mix

leads to

2021-12-28 12:28:19.269 [massa-001@127.0.0.1]:[pid=<0.652.0> ]:[error]:GenServer MassaProxy.Orchestrator terminating
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: not an integer

    :erlang.send_after("3000", #PID<0.652.0>, :work)
    (massa_proxy 0.1.0) lib/massa_proxy/orchestrator.ex:52: MassaProxy.Orchestrator.schedule_work/1
    (massa_proxy 0.1.0) lib/massa_proxy/orchestrator.ex:47: MassaProxy.Orchestrator.handle_info/2
    (stdlib 3.17) gen_server.erl:695: :gen_server.try_dispatch/4
    (stdlib 3.17) gen_server.erl:771: :gen_server.handle_msg/6
    (stdlib 3.17) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: :work
State: []
``