Add testing as an alias to 7.0

Author: ericholscher

readthedocs/settings/base.py

@@ -424,7 +424,7 @@ def USE_PROMOS(self):  # noqa
                 },
             },
         },
-        'readthedocs/build:testing': {
+        'readthedocs/build:7.0': {
             'python': {
                 'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7, 3.8, 'pypy3.5'],
                 'default_version': {
@@ -439,6 +439,7 @@ def USE_PROMOS(self):  # noqa
     DOCKER_IMAGE_SETTINGS.update({
         'readthedocs/build:stable': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:5.0'),
         'readthedocs/build:latest': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:6.0'),
+        'readthedocs/build:testing': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:7.0'),
     })
 
     # All auth