Make regexps adapt to newer error messages in SQLite 3.8

Hi,

It seems that SQLite 3.8.2+ changed their error message formats for unique, foreign key and not null constraints. 
That makes spec/integration/database_test.rb fail:
```
1) Sequel::Database constraint violations should raise Sequel::UniqueConstraintViolation when a unique constraint is violated
   Failure/Error: Unable to find matching line from backtrace
     expected Sequel::UniqueConstraintViolation, got #<Sequel::DatabaseError: SQLite3::ConstraintException: UNIQUE constraint failed: test.a> with backtrace:
       # ./lib/sequel/adapters/sqlite.rb:181:in `block (2 levels) in _execute'
       # ./lib/sequel/database/logging.rb:33:in `log_yield'
...
```
So I did a small modification to fix it. Hope it can help!