BUG(cli): crash with explicit config file names (#113)

Fixes a bug where passing an explicit config file name crashes the
argument parsing.

Closes: #112

heracles/cli.py

@@ -734,7 +734,6 @@ def add_command(func):
     cmd_parser.add_argument(
         "-c",
         "--config",
-        default="heracles.cfg",
         help="configuration file (can be repeated)",
         metavar="<config>",
         action="append",
@@ -861,6 +860,10 @@ def add_command(func):
         main_parser.print_help()
         return 1
 
+    # fix default config
+    if not args.files:
+        args.files = ["heracles.cfg"]
+
     # get keyword args
     kwargs = vars(args)
     cmd = kwargs.pop("cmd")