Fix cache_dir() problem, made it configurable

src/gmhc_config_schema.erl

@@ -1,5 +1,5 @@
 -module(gmhc_config_schema).
--vsn("0.6.1").
+-vsn("0.8.3").
 
 -export([ schema/0
         , to_json/0
@@ -51,6 +51,7 @@ schema() ->
          , pool => pool()
          , pool_admin => pool_admin()
          , workers => workers()
+         , cache_dir => str(#{description => <<"Location of cache, default is 'setup:data_dir()'">>})
          , report => str(#{ enum  => [<<"debug">>, <<"progress">>, <<"silent">>]
                           , default => <<"silent">>
                           , description => <<"Progress reporting">> })