Bump future from 0.18.2 to 0.18.3

Bumps [future](https://github.com/PythonCharmers/python-future) from 0.18.2 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@v0.18.2...v0.18.3)

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

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

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@ coveralls==1.11.1; python_version <= '3.5'
 coveralls==3.3.1; python_version > '3.5'
 flake8<3.7
 flake8-per-file-ignores==0.8.1
-future==0.18.2
+future==0.18.3
 graphene==3.1.1
 promise==2.3
 mongoengine==0.19.1; python_version <= '3.5'