Make model association step more idiomatic

[morenoh149]

• use Object.values to get a more meaningful model var and associate it if it has an associate field.

[Sharlaan]

Another variant, bit more "functional" :

  Object.values(models)
    .filter(model => typeof model.associate === 'function')
    .forEach(model => model.associate(models));

[morenoh149]

@Sharlaan I also considered

 Object.values(models)
    .filter(model => model.associate)
    .forEach(model => model.associate(models));

and

 Object.values(models).forEach(model => model.associate && model.associate(models));

but I preferred my proposal as most understandable.

[rwieruch]

Thanks for the input! I will take this into account once I write a new version for the tutorial 🚀 Given that it will take some time, please leave your suggestions here on how to make it more idiomatic!