Milo: Fix naming of pubsub settings

milo/common/config/settings.proto

Index: milo/common/config/settings.proto
diff --git a/milo/common/config/settings.proto b/milo/common/config/settings.proto
index e98375695a5ae22c7ac087a7efdbe1e3446d4a86..9789a4e7787040992b14741084c7f38c0eb1c0bb 100644
--- a/milo/common/config/settings.proto
+++ b/milo/common/config/settings.proto
@@ -13,13 +13,13 @@ message Settings {
     // buildbot data.
     string internal_reader = 1;
 
-    // public_topic is the name of the pubsub topic where public builds come in
+    // public_subscription is the name of the pubsub topic where public builds come in
     // from
-    string public_topic = 2;
+    string public_subscription = 2;
 
-    // internal_topic is the name of the pubsub topic where internal builds
+    // internal_subscription is the name of the pubsub topic where internal builds
     // come in from
-    string internal_topic = 3;
+    string internal_subscription = 3;
   }
   Buildbot buildbot = 1;