Bump cffi from 1.12.3 to 1.13.0

Bumps [cffi](https://bitbucket.org/cffi/release-doc) from 1.12.3 to 1.13.0.
- [Commits](https://bitbucket.org/cffi/release-doc/commits)

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

test-requirements.txt

@@ -11,7 +11,7 @@ async-generator==1.10
 atomicwrites==1.3.0       # via pytest
 attrs==19.1.0
 backcall==0.1.0           # via ipython
-cffi==1.12.3              # via cryptography
+cffi==1.13.0              # via cryptography
 coverage==4.5.4           # via pytest-cov
 cryptography==2.7         # via pyopenssl, trustme
 decorator==4.4.0          # via ipython, traitlets