Update to 0.8.1.
- Fixed precedence issue for f-string expressions that caused redundant parenthesis around expression.
- Fixed astor.to_source() incorrectly checking whether source_generator_class is a subclass of astor.code_gen.SourceGenerator.
- Fixed TypeError when AST nodes with unicode strings are passed to astor.to_source().
- Fixed installation issue with setuptools 41.4.0 or later due to the use of an undocumented feature.