#389 DuplicateKeyError has invalid base class

[Łukasz Rogalski]

https://sourceforge.net/p/ruamel-yaml/code/ci/default/tree/constructor.py#l54
Base class for raised exception is incorrect (should be MarkedYAMLError).

This interferes with pre-commit-hooks (uncaught exception) which then leaks stack trace to user.
https://github.com/pre-commit/pre-commit-hooks/blob/master/pre_commit_hooks/check_yaml.py#L64

While technically malfunction could be mitigated in pre-commit-hook, it's clear bug in runamel.yaml

Uncovered during running pre-commit-hooks / check-yaml on legacy codebase.

[Anthon van der Neut]

This should be fixed in 0.17.11