Bump fireworks from 1.8.7 to 1.9.4

Bumps [fireworks](https://github.com/materialsproject/fireworks) from 1.8.7 to 1.9.4.
- [Release notes](https://github.com/materialsproject/fireworks/releases)
- [Changelog](https://github.com/materialsproject/fireworks/blob/master/docs/changelog.html)
- [Commits](materialsproject/fireworks@v1.8.7...v1.9.4)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements_dev.txt

@@ -1,5 +1,5 @@
 # Requirements of this dev
-FireWorks==1.8.7
+FireWorks==1.9.4
 GitPython==2.1.11
 black==19.3b0
 flake8==3.7.8