Update Ansible version requirement in README (1.6+)
Update Ansible version requirement in README (1.6+)

maurizi/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,azavea/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees,RickMohr/nyc-trees,kdeloach/nyc-trees,maurizi/nyc-trees,RickMohr/nyc-trees,azavea/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees,kdeloach/nyc-trees,RickMohr/nyc-trees,RickMohr/nyc-trees,maurizi/nyc-trees,maurizi/nyc-trees