Bump cython from 0.28.1 to 0.29.3 (#48)

Bumps [cython](https://github.com/cython/cython) from 0.28.1 to 0.29.3.
- [Release notes](https://github.com/cython/cython/releases)
- [Changelog](https://github.com/cython/cython/blob/master/CHANGES.rst)
- [Commits](https://github.com/cython/cython/compare/0.28.1...0.29.3

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

requirements.dev.txt

 flake8==3.5.0
-Cython==0.28.1
+Cython==0.29.3
 nose==1.3.7
 pycodestyle==2.3.1
 pylint==1.8.3