Merge branch 'bochecha/blessings' into 'bst-1.2'

deps: Specify the minimum version required for blessings

See merge request !663

setup.py

@@ -261,7 +261,7 @@ setup(name='BuildStream',
           'ruamel.yaml < 0.15.52',
           'pluginbase',
           'Click',
-          'blessings',
+          'blessings >= 1.6',
           'jinja2 >= 2.10',
           'protobuf >= 3.5',
           'grpcio >= 1.10',