Update dependencies in requirements_dev.txt (#188)
Update dependencies in requirements_dev.txt (#188)

The following updates were done by pyup-bot:

- Update pytest from 3.6.3 to 3.6.4 (#184)
- Update pip from 10.0.1 to 18.0 (#178)
- Update cryptography from 2.2.2 to 2.3 (#173)
- Update sphinx from 1.7.5 to 1.7.6 (#166)
- Update tox from 3.0.0 to 3.1.2 (#162)

ljvmiranda921/pyswarms,ljvmiranda921/pyswarms