test whether shiny app actually runs

[maxheld83]

currently as in https://github.com/subugoe/hoad/commit/c7c69940357ac69d9bae79669adf2e8c4652bab6 and others, the app/dashboard isn't actually tested as part of the CI. It just gets deployed, and then the deploy fails, which is hard to debug.

There needs to be a test here, for starters just whether the app can run and then some proper testing as per #8