bumped version

Author: dave-doty

lib/src/constants.dart

@@ -9,7 +9,7 @@ import 'state/grid.dart';
 
 // WARNING: Do not modify line below, except for the version string
 //          (and also add new version string to scadnano_versions_to_link).
-const String CURRENT_VERSION = "0.20.0";
+const String CURRENT_VERSION = "0.20.1";
 const String INITIAL_VERSION = "0.1.0";
 
 // scadnano versions that we deploy so that older versions can be used.