Bump pynacl from 1.3.0 to 1.4.0

Bumps [pynacl](https://github.com/pyca/pynacl) from 1.3.0 to 1.4.0.
- [Release notes](https://github.com/pyca/pynacl/releases)
- [Changelog](https://github.com/pyca/pynacl/blob/master/CHANGELOG.rst)
- [Commits](pyca/pynacl@1.3.0...1.4.0)

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

requirements-pinned.txt

@@ -4,7 +4,7 @@ cryptography==2.9.2
 enum34==1.1.6             ; python_version < "3" # via cryptography
 ipaddress==1.0.23         ; python_version < "3" # via cryptography
 pycparser==2.20           # via cffi
-pynacl==1.3.0
+pynacl==1.4.0
 python-dateutil==2.8.1
 six==1.14.0
 subprocess32==3.5.4       ; python_version < "3"