Update PyYAML version (CVE-2017-18342)

[frantsao]

Prerequisites

• [X ] Put an X between the brackets on this line if you have done all of the following:
  • Checked that your issue isn't already filled: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aidealista
  • Checked that there is not already provided the described functionality

Description

Current PyYAML stable release (3.1.3) needed for molecule tests, has a security issue: CVE-2017-18342.

Versions

1.0

Additional Information

PyYALM developers are planning to release soon a new stable version:
yaml/pyyaml#193
We'll wait until this release for fixing it.