[5.8] Fix UPDATE queries with alias

[staudenmeir]

PostgreSQL and SQLite don't support UPDATE queries with qualified column names in the SET clause.

We are already removing the table name, but that doesn't work with an alias:

DB::table('comments as c')
    ->join('posts as p', 'p.id', '=', 'c.post_id')
    ->where('p.active', 0)
    ->update(['c.active' => 0]);

update "comments" as "c" set "c"."active" = 0
from "posts" as "p"^         ^^^^
where "p"."active" = 0 and "p"."id" = "c"."post_id"

We can cover both cases by just taking everything after the dot.