Fix GenEvent detecting module that isn't loaded

Signed-off-by: José Valim <[email protected]>

Author: fishcakez

lib/elixir/lib/gen_event.ex

@@ -1015,7 +1015,7 @@ defmodule GenEvent do
       case reason do
         {:undef, [{m,f,a,_}|_]=mfas} ->
           cond do
-            :code.is_loaded(m) ->
+            :code.is_loaded(m) === false ->
               {:"module could not be loaded", mfas}
             function_exported?(m, f, length(a)) ->
               reason