Fix review comments.

letsencrypt/cli.py

@@ -454,7 +454,6 @@ def create_parser(plugins, args):
     #    subparser.add_argument("domains", nargs="*", metavar="domain")
     helpful.add(None, "-d", "--domains", metavar="DOMAIN", action="append")
 
-
     helpful.add_group(
         "automation",
         description="Arguments for automating execution & other tweaks")

letsencrypt/plugins/manual.py

@@ -11,20 +11,19 @@ from acme import challenges
 from acme import jose
 
 from letsencrypt import interfaces
-from letsencrypt.plugins import null
+from letsencrypt.plugins import common
 
 
 logger = logging.getLogger(__name__)
 
 
-class ManualAuthenticator(null.Installer):
+class ManualAuthenticator(common.Plugin):
     """Manual Authenticator.
 
     .. todo:: Support for `~.challenges.DVSNI`.
 
     """
-    zope.interface.implements(
-        interfaces.IAuthenticator, interfaces.IInstaller)
+    zope.interface.implements(interfaces.IAuthenticator)
     zope.interface.classProvides(interfaces.IPluginFactory)
 
     description = "Manual Authenticator"