Please pin pyyaml to 3.13 until the pyyaml 5.1 fixes are done for python 3.7 support

[bryder]

pyyaml-3.12 will not build the c extensions when using python 3.7 so I can not build curator using python 3.7.

pyyaml-3.13 added support for python-3.7 but curator is pinned to 3.12 at the moment.

reference to changes in pyyaml

This relates to #1368

Expected Behavior

pyyaml-3.13 should be the requirement so curator can be used with python 3.7

Actual Behavior

I can not build curator using python 3.7 if the requirements are respected

Steps to Reproduce the Problem

I use an internal build system behind a firewall so can't easily show the steps here.

I suspect installing python 3.7 and building with pip will show the error when trying to build pyyaml-3.12 which emit the same errors I've been getting but unfortunately I can't do that from where I am.

Specifications

• Version: curator 5.7.6
• Platform: ubuntu 16.04/18.04, Python 3.7.3

[untergeek]

This is done. Curator 5.8 is currently pinned ti pyyaml=3.13