Bump gevent from 1.4.0 to 1.5.0

Bumps [gevent](https://github.com/gevent/gevent) from 1.4.0 to 1.5.0.
- [Release notes](https://github.com/gevent/gevent/releases)
- [Changelog](https://github.com/gevent/gevent/blob/master/docs/changelog_1_4.rst)
- [Commits](gevent/gevent@1.4.0...1.5.0)

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