cloudfriend is incompatible with cfn-lint > 0.51.0

[bilindhajer]

cfn-lint (a python package) is used for tests in cloudfriend, any version > 0.51.0 causes tests to break. Currently it is hardcoded to 0.51.0 (https://github.com/mapbox/cloudfriend/blob/master/.travis.yml#L6), this ticket is for doing the necessary work to get the tests working with the latest version of cfn-lint.