Bump future from 0.18.0 to 0.18.1

Bumps [future](https://github.com/PythonCharmers/python-future) from 0.18.0 to 0.18.1.
- [Release notes](https://github.com/PythonCharmers/python-future/releases)
- [Changelog](https://github.com/PythonCharmers/python-future/blob/master/docs/changelog.rst)
- [Commits](https://github.com/PythonCharmers/python-future/commits)

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

requirements/base.txt

@@ -18,7 +18,7 @@ requests==2.22.0
 static==1.1.1
 whitenoise[brotli]==4.1.4
 urllib3[secure]==1.25.6
-future==0.18.0
+future==0.18.1
 coreapi==2.3.3
 Markdown==3.1.1
 pygments==2.4.2