Bump future from 0.16.0 to 0.18.3

Bumps [future](https://github.com/PythonCharmers/python-future) from 0.16.0 to 0.18.3.
- [Release notes](https://github.com/PythonCharmers/python-future/releases)
- [Changelog](https://github.com/PythonCharmers/python-future/blob/master/docs/changelog.rst)
- [Commits](PythonCharmers/python-future@v0.16.0...v0.18.3)

---
updated-dependencies:
- dependency-name: future
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -23,7 +23,7 @@ responses
 httpretty
 astroquery >= 0.4 # Needed for halophot
 autograd == 1.4 # Needed for halophot
-future == 0.16.0 # Needed for halophot
+future == 0.18.3 # Needed for halophot
 halophot == 0.7.6.1
 jplephem >= 2.9
 spiceypy == 5.0.1