[fenix] Bump future from 0.18.2 to 0.18.3 in /taskcluster

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](https://github.com/PythonCharmers/python-future/compare/v0.18.2...v0.18.3)

---
updated-dependencies:
- dependency-name: future
  dependency-type: indirect
...

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

taskcluster/requirements.txt

@@ -22,8 +22,8 @@ charset-normalizer==2.1.1 \
     --hash=sha256:5a3d016c7c547f69d6f81fb0db9449ce888b418b5b9952cc5e6e66843e9dd845 \
     --hash=sha256:83e9a75d1911279afd89352c68b45348559d1fc0506b054b346651b5e7fee29f
     # via requests
-future==0.18.2 \
-    --hash=sha256:b1bead90b70cf6ec3f0710ae53a525360fa360d306a86583adc6bf83a4db537d
+future==0.18.3 \
+    --hash=sha256:34a17436ed1e96697a86f9de3d15a3b0be01d8bc8de9c1dffd59fb8234ed5307
     # via mozilla-version
 giturlparse==0.10.0 \
     --hash=sha256:04ba1a3a099c3093fa8d24a422913c6a9b2c2cd22bcffc939cf72e3e98f672d7 \