Fix autodetection of rpmautospec

When store_true or store_false are used, the default default changes
from None to a boolean. I didn't know about this, and I wrote the code
to assume args.rpmautospec would be None. rpmautospec detection was
effectively always disabled.

rust2rpm/__main__.py

@@ -360,8 +360,10 @@ def main():
     parser.add_argument("-s", "--store-crate", action="store_true",
                         help="Store crate in current directory")
     parser.add_argument("-a", "--rpmautospec", action="store_true",
+                        default=None,
                         help="Use autorelease and autochangelog features")
     parser.add_argument("--no-rpmautospec", action="store_false",
+                        default=None,
                         help="Do not use rpmautospec")
     parser.add_argument("--relative-license-paths", action="store_true",
                         help="Put all license files in main license directory")