feat(query-builder): add last method

[RomainLanz]

Closes #214

[thetutlage]

Why latest and not last? Since we already use first

[RomainLanz]

It feels more "English" in my head but I may be wrong!
Do you want me to update it to last?

[webdevian]

First & Last pair nicely, the opposite of Latest would be Earliest or Oldest

[RomainLanz]

Updated 👍

[coveralls]

Coverage decreased (-0.1%) to 96.238% when pulling 45fe060 on RomainForks:feature/query-builder-last into fe69ed2 on adonisjs:develop.

[thetutlage]

@RomainLanz Can u add the other methods too. So this is how it should be

1. Database query builder, should have the last method and make use of id to add the orderBy clause.

2. Model query builder should use primaryKey for the orderByClause

3. Model static method, just calls the query builder method.

And the orderBy field can be overridden as it is in your code already

[RomainLanz]

Should be good 👍

[coveralls]

Coverage decreased (-0.08%) to 96.266% when pulling 641803e on RomainForks:feature/query-builder-last into fe69ed2 on adonisjs:develop.