Add and apply LineContinuationSpacing rubocop rule

So now we're consistent when separating multiline strings.

spec/system/admin/administrators_spec.rb

@@ -35,7 +35,7 @@ describe "Admin administrators" do
   scenario "Delete Administrator" do
     visit admin_administrators_path
 
-    confirmation = "Are you sure? This action will delete "\
+    confirmation = "Are you sure? This action will delete " \
                    "\"#{user_administrator.name}\" and can't be undone."
 
     within "#administrator_#{user_administrator.id}" do