fix: migration generator indexes

[nickschot]

A single index was created over id, created_at and updated_at in the default generator for migrations. This also gave problems with mysql (index too long).

[nickschot]

Will probably need to modify the migrations of the example applications too. But I'll do that tomorrow.

[codecov-io]

Current coverage is 91.92% (diff: 100%)

Merging #625 into master will not change coverage

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[nickschot]

Ugh, this is still wrong. Only way to do it is to set the indexes separately.

[zacharygolba]

So I've been thinking about this and I think we're better off adding timestamp indexes individually.

table.timestamps();
table.index('created_at');
table.index('updated_at');

Also, we can remove the additional index on id as it should already be covered as the primary key.

[zacharygolba]

I don't think we have to create an additional index for id as it will be the primary key.

[nickschot]

Indeed. That is covered. I noticed the need for separate indexes too in the comment before this. Knex has no API to add multiple indexes at once. I'll try to work on this a bit later tonight.

[zacharygolba]

👍 Sounds good.

[zacharygolba]

👏 This looks good @nickschot. One last thing though. Can you update the migrations in the examples as well as the test-app?