Bump future from 0.17.1 to 0.18.3

Bumps [future](https://github.com/PythonCharmers/python-future) from 0.17.1 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@v0.17.1...v0.18.3)

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

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

requirements.txt

@@ -1,2 +1,2 @@
 boto3==1.7.2
-future==0.17.1
+future==0.18.3