Default to keeping user's email addresses private.

db/migrate/20180924221715_user_email_public_defaults_to_false.rb

@@ -0,0 +1,9 @@
+class UserEmailPublicDefaultsToFalse < ActiveRecord::Migration[5.0]
+  def up
+    change_column_default :users, :email_public, false
+  end
+
+  def down
+    change_column_default :users, :email_public, true
+  end
+end