railsrc: Skip tests when building new application (#744)

Follow-up to #728

In an effort to create parity with the [upcoming release of
Suspenders][1], we pass the `--skip-test` argument when running [rails
new][2].

This means if you're using our `railsrc` file, you would just need to
pass the `-m` argument when generating a new Rails application.

[1]: thoughtbot/suspenders#1135
[2]: https://guides.rubyonrails.org/command_line.html#rails-new

railsrc

@@ -1 +1,2 @@
 --database=postgresql
+--skip-test