Release Docker image 6.0

Mark
 - 5.0 as stable
 - 6.0 as latest

Author: humitos

readthedocs/settings/base.py

@@ -413,7 +413,7 @@ def USE_PROMOS(self):  # noqa
                 },
             },
         },
-        'readthedocs/build:6.0rc1': {
+        'readthedocs/build:6.0': {
             'python': {
                 'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7, 3.8, 'pypy3.5'],
                 'default_version': {
@@ -426,8 +426,8 @@ def USE_PROMOS(self):  # noqa
 
     # Alias tagged via ``docker tag`` on the build servers
     DOCKER_IMAGE_SETTINGS.update({
-        'readthedocs/build:stable': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:4.0'),
-        'readthedocs/build:latest': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:5.0'),
+        'readthedocs/build:stable': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:5.0'),
+        'readthedocs/build:latest': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:6.0'),
     })
 
     # All auth