build(deps-dev): bump pyaml from 18.11.0 to 19.4.1

Bumps [pyaml](https://github.com/mk-fg/pretty-yaml) from 18.11.0 to 19.4.1.
- [Release notes](https://github.com/mk-fg/pretty-yaml/releases)
- [Commits](https://github.com/mk-fg/pretty-yaml/commits)

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

requirements/dev.txt

@@ -5,7 +5,7 @@ hg+https://nicfit@bitbucket.org/nicfit/sphinxcontrib-bitbucket
 ipdb==0.11
 nicfit.py[cookiecutter]==0.8.3
 pss==1.42
-pyaml==18.11.0
+pyaml==19.4.1
 sphinx-issues==1.2.0
 sphinx_rtd_theme==0.4.3
 tox==3.14.0