Fix default value for subject_alternative_names

[oriondevelops]

The 'subject_alternative_names' column in the migration had a default value of an empty JSON array as a string, which caused an error when running the migration. This PR fixes the error by updating the default value to use an Expression as documented here.

Using an Expression instance will prevent Laravel from wrapping the value in quotes and allow you to use database
specific functions. One situation where this is particularly useful is when you need to assign default values to JSON
columns.

Fixes #29

[Daanra]

Thank you!

[ericbae]

I'm still getting an error

SQLSTATE[42883]: Undefined function: 7 ERROR: function json_array() does not exist HINT: No function matches the given name and argument types. You might need to add explicit type casts. (Connection: pgsql, SQL: alter table "lets_encrypt_certificates" add column "subject_alternative_names" json not null default (JSON_ARRAY()))

I'm running on Laravel 10 and PostgreSQL 14. In fact, in Postgres, the previous default value works well. which was default('[]')

[Daanra]

@ericbae For now, you can edit the migration after publishing it.

If anyone knows how to make this work for all databases, I'd appreciate a PR.