Require Ansible v2.7 or newer (because of items2dict and dict2items)

Interestingly, no one has reported this failure before #662 (Github
Issue).

It doesn't make sense to keep saying that we support such old Ansible
versions, when we're not even testing on anything close to those.

Time is also passing and such versions are getting more and more
ancient. It's time we bumped our requirements to something that is more
likely to work.

docs/ansible.md

@@ -9,7 +9,7 @@ If your local computer cannot run Ansible, you can also run Ansible on some serv
 
 ## Supported Ansible versions
 
-Ansible 2.5.2 or newer is required.
+Ansible 2.7.0 or newer is required.
 
 
 ## Checking your Ansible version
@@ -49,7 +49,7 @@ docker run -it --rm \
 -v `pwd`:/work \
 -v $HOME/.ssh/id_rsa:/root/.ssh/id_rsa:ro \
 --entrypoint=/bin/sh \
-devture/ansible:2.9.9-r0
+devture/ansible:2.9.13-r0
 ```
 
 The above command tries to mount an SSH key (`$HOME/.ssh/id_rsa`) into the container (at `/root/.ssh/id_rsa`).